This dissertation has been 64—1291 microfilmed exactly as received

NOVOTNY, Robert Frank, 1926- BEDROCK GEOLjOGY OF THE DOVER-EXETER- PORTSMOUTH REGION, NEW HAMPSHIRE.

The Ohio State University, Ph.D., 1963 G eology

University Microfilms, Inc., Ann Arbor, Michigan BEDROCK GEOLOGY

OF THE

DOVER-EXETER-PORTSMOUTH REGION,

NEW HAMPSHIRE

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By

Robert Frank Novotny, A. B., M. S.

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The Ohio State University 1963

Approved by

Adviser ' Department of Geology ACKNOWLEDGMENTS

The writer owes a great debt of gratitude to Professor

Carl A* Lamey of the Department of Geology, The Ohio State University, who gave so unstintingly of his time and invaluable counsel during the course of the investigation. Sincere thanks are also due

Professor T, R. Meyers, State Geologist of New Hampshire and faculty member, Department of Geology, University of New Hampshire, who most generously provided the writer with notes and information concern­ ing his knowledge of the geology of southeastern New Hampshire amassed over a period of many years. Greatly appreciated, also, is the information and encouragement given the writer, both in the field and in the laboratory, by Professor Marland P. Billings, Harvard

University; Dr. Lincoln R. Page and Mr. Norman P. Cuppels, United

States Geological Survey; Dr. Jane L. Forsyth, Ohio Geological

Survey; and Professors Richard P. Goldthwait, George E. Moore, and

Sidney E. White, The Ohio State University.

The writer is also indebted to Dr. and Mrs. John D. Winslow,

United States Geological Survey, for the photomicrographs included in the report, and to Mrs. Gertrude M. Scheibel, United States

Geological Survey, for her part in the final preparation of the manuscript.

The writer is also thankful for the financial assistance of the Geological Society of America; the Department of Geology, The

Ohio State University; the American Academy of Arts and Sciences; and the State of New Hampshire, without whose aid the study could not have been undertaken.

iii TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS...... ii

LIST OF TABLES ...... viii

LIST OF ILLUSTRATIONS...... i*

INTRODUCTION ...... 1

Location and Extent of A r e a ...... 1 Previous Work in the A r e a ...... 3 Field W o r k ...... 3 Geomorphology and Glacial Geology ...... 4 Statement of P r o b l e m . 8

GENERAL STRATIGRAFHIC RELATIONS ...... 9

General Statement ...... 9 Rye Formation (Ordovician?)...... 11 General statement...... 11 Lower metasedimentary m e m b e r ...... 13 General statement ...... • . 13 Schists . * * ...... 14 Quartzites 19 Amphibolites...... 22 Upper metavolcanic member ...... 25 General statement ...... 25 Metavolcanic rocks ...... 26 Metasedimentary rocks ...... 33 Injection and permeation gneiss ...... 38 Kittery Formation (Silurian?) ...... 46 General statement ...... 46 S l a t e s ...... 51 Phyllites...... 53

iv TABLE OF CONTENTS - Continued

Page

Schists ...... 54 Q u a r t e t t e s ...... 58 Lime-silicate rocks ...... 60 Eliot Formation (Silurian?) ...... 62. General statement...... 62 S l a t e s ...... 64 Phyllites...... 66 S c h i s t s ...... 70 Q u a r t e t t e s ...... 72 Lime-silicate rocks ...... 74 Berwick Formation (Silurian?) ...... 75 General statement...... 75 S c h i s t s ...... 77 Lime-silicate rocks ...... 81 Littleton Formation (Devonian) ...... 83

INTRUSIVE IGNEOUS ROCKS ...... 87

General Statement ...... 87 Hillsboro Plutonic Series .... . 88 General statement ...... 88 Breakfast Hill granite and pegmatite ...... 89 Newburyport quartz diorite ...... 99 Porphyritic quartz monzonite ...... 108 Exeter diorite ...... 116 General statement ...... 116 Gabbro ...... 121 D i o r i t e ...... 123 Quartz diorite ...... 126 Quartz monzonite...... 128 Granite and apllte dikes ...... 130 Quartz monzonite ...... 132 White Mountain Plutonic-Volcanlc S e r i e s ...... 136 General statement...... * ...... 136 C a m p t o n i t e ...... 136 G r a n o p h y r e ...... 141 v TABLE OF CONTENTS - Continued

Page

STRUCTURAL GEOLOGY ...... 142

General Statement ...... • . . . 142 Folds ...... 143 General statement ...... • . 143 Rye anticline . . • 143 Great Bay syncline...... 144 Exeter anticline ...... 145 F a u l t s ...... 146 General statement ...... 146 Portsmouth fault ...... 146 Seabrook thrust ...... 147 Minor structural features ...... 148 General statement • • • . • • . • . 148 Minor folds ...... 149 Cleavage...... 130 Schistosity ...... 131 Lineation ...... 131 Joints ...... 152

METAMORPHISM ...... 157

General Statement ...... 157 Metamorphic Zonation ...... 138 Time of Metamorphism...... 160 Causes of Metamorphism 161

STRATIGRAPH1C CORRELATIONS ...... 163

General Statement ...... 163 Correlation with Eastern and East-Central Massachusetts • 163 Correlation with Southwestern Maine ...... ■ 165 Correlation with Western New Hampshire ...... 166 Evidence from Igneous R o c k s ...... 167 Conclusions ...... 168

vi TABLE OF CONTENTS - Continued

Page

SUMMARY OF GEOLOGIC HISTORY ...... 169

ECONOMIC GEOLOGY ...... 172

REFERENCES ...... 174

AUTOBIOGRAPHY...... 182

vii LIST OF TABLES

(All cables are in pocket)

Table

1. Approximate Modes of the Lower Member of the Rye Formation

2. Approximate Modes of the Upper Member of the Rye Formation

3. Approximate Modes of the Kittery Formation

4. Approximate Modes of the Eliot Formation

5. Approximate Modes of the Berwick and Littleton Formations

6. Approximate Modes of the Hillsboro Plutonic Series

7. Approximate Modes of the Hillsboro Plutonic Series

8. Approximate Modes of the White Mountain Plutonic Series

viii LIST OF ILLUSTRATIONS

Figure Fage

1. Location of A r e a ...... 2

2. Contour Diagram of Camptonite Dikes and Sills • . • 139

3. Contour Diagram of Joints in the Rye Formation • . 153

4. Contour Diagram of Joints in the Kittery Formation 154

5. Contour Diagram of Joints in the Breakfast Hill Granite and Pegmatite 155

Plate Page

I. Geologic Hap and Structure Sections (in pocket)

II. Outcrop of Permeation and Injection Gneiss, with Relict Bedding ...... 39

III. Outcrop of Permeation and Injection Gneiss, Showing Large Feldspar A u g e n ...... 40

IV. Photomicrograph of Permeation and Injection Gneiss 45

V. Outcrop of Crinkled Kittery Formation ...... 50

VI. Outcrop of Folded Eliot Formation ...... 67

VII. Photomicrograph of Dolomite Porphyroblast in Eliot Formation 68

VIII. Photomicrograph of Incipient Cleavage in Eliot Formation...... 69

ix LIST OF ILLUSTRATIONS - Continued

Plate Page

IX. Photomicrograph of Berwick Formation, Showing Biotite Porphyroblasts ...... > 79

X. Photomicrograph of Berwick Formation, Showing Actinolite Porphyroblasts ...... 84

XI. Outcrop of Breakfast Hill Pegmatite Lens in Lower Member of the Rye F o r m a t i o n ...... 92

XII. Outcrop of Folded Breakfast Hill Pegmatite in the Lower Member of the RyeFo r m a t i o n ...... 93

XIII. Camptonite Dikes in Lower Member of the Rye Formation ...... 138

x INTRODUCTION

Location and Extent of Area

The Dover-Exeter•Portsmouth area of this investigation consti­ tutes approximately 225 square miles in southeastern New Hampshire and includes the New Hampshire portions of the Dover (1913), Exeter (1934), and York (1920) quadrangles of the United States Geological Survey

fifteen-minute topographic map series.

A ramifying network of secondary roads, in addition to the two arterial north-south highways, Lafayette Road (U. S. Route 1) and the

New Hampshire Turnpike, makes the region readily accessible. The

Boston and Maine Railroad provides north-south rail transportation

through Exeter, Dover, Hampton, and Portsmouth.

Industry is concentrated in the towns of Dover, Portsmouth,

Newmarket, and Exeter. Portsmouth Harbor serves as a base for fish­

ing operations and is the site of the Portsmouth Navy Yard. Pease

Air Force Base, which is located approximately two miles west- northwest of the city of Portsmouth, is also a source of civilian

employment. (The air base was established within the past ten years,

hence it does not appear on the Dover topographic map.) Other

significant means of livelihood are dairy and poultry farming and the

operation of summer resorts.

Figure 1 shows the location of the area mapped.

1 Figure 1.— Location of area. 3

Previous Work in the Are*

Early contributions to the knowledge of the bedrock geology of

southeastern New Hampshire include the work of Jackson (1841, 1844),

Hitchcock (1874, 1877, 1878), Katz (1917), and Wsndke (1922). More

recently Meyers (1940) summarized the results of his studies in the

Dover quadrangle. Billings (1952, 1956) assembled the materials

for maps and texts first of southern New Hampshire and then the entire

state. Data for the coastal region were based on reconnaissance work by Billings and on information supplied by Professor T* R. Meyers

of the University of New Hampshire.

Field Work

The sumners of 1953 and 1954 were spent in geologic mapping,

using as base maps United States Geological Survey topographic sheets

enlarged to a scale of two inches to one mile. Inspection, and pace

and compass traverses were used in locating outcrops. The geologic

map, Plate 1 (in pocket), is a result of the investigation.

Many hand specimens were collected and from them 500 thin sections

were prepared and studied. An additional 50 thin sections were

loaned to the author by Professor T. R. Meyers of the University of

New Hampshire. Geotnorphology and Glacial Geology

The area under consideration is situated in the Seaboard Lowland section of the New England physiographic province (Fenneman, 1938, pi. 1) and is characterized by low relief. The maximum relief is 200 feet, the average is from 30 to 100 feet. The topography is typically that formed by mature dissection modified by glacial deposits.

Drainage patterns commonly suggest a moderate degree of control by the underlying metamorphic rocks, which generally strike northeast.

Tide waters flush several of the larger channels as far inland as

Dover, Durham, Exeter, Newmarket, and Salmon Falls.

Studies concerning the geomorphology and glacial geology of southeastern New Hampshire date to 1844, but the more comprehensive and accurate works are those of the past 50 years. Outstanding among these investigations are the works of Katz and Keith (1917),

J. W. Goldthwait (1925, 1938), and J. W. Goldthwait et al (1951).

Although at least two probable substages of Wisconsin glaciation are represented in other parts of New England by two tills

(J. W. Goldthwait et al, 1951, p. 20), such evidence is lacking in

southeastern New Hampshire, where only one gray to brown-gray till is known to exist. The thickness of the till has been reported to be as much as 220 feet in a drumlin in Kensington by Meyers and Bradley

(1960, p. 11). 5

Drumlins and drumlinoid hills, with a southeasterly orien­ tation, are erratically distributed throughout the area, but are distinctly clustered in the townships of Kensington, East Kensington, and South Hampton. Great Boar's Head, north of Hampton Beach, which was once an island drumlin, is now tied to the mainland and is partially eroded by shoreline processes.

Overlying the till in much of the area is stratified sand and gravel that occurs in outwash plains, kames, kame terraces, and kame plains. Ice contact features such as slumping and crumpling have been noted by Tuttle (1952, p. 68).

Outwash plains or remnants of them are few and dubious, according to Tuttle (1952, p. 78), and only the flat sandy plain south of

Portsmouth is regarded as representative. Kames are also rare and only the knob on Fox Point, Newington, is thus identified. Kame

terraces, on the other hand, are relatively abundant, existing pri­ marily as plain surfaces of bedded sand and gravel contiguous to drumlins and drumlinoid hills. Typical of this group are the

terrace forms associated with Stratham Heights and Rollins Hill in

Stratham and Bride Hill in Hampton. Tuttle (1952, p. 69) includes

The Hoppers of Barrington, Rochester, and Dover in this category.

In 1938 J. W. Goldthwait revised an earlier opinion (1925),

that the disappearance of ice from southeastern New Hampshire was

accomplished by systematic melting back of the ice front, to an

hypothesis of ice stagnation. 6

Katz and Keith (19X7) , investigating surficial geology in the Dover-Exeter-Portsraouth area, mapped an elongate north-south trending moraine, the Newington moraine, from southwestern Maine into northeastern Massachusetts on the assumption of normal ice front recession. Tuttle (1952, p. 53-74), adhering to Goldthwait1s hypothesis, reclassified the Newington moraine and several other stratified sand and gravel deposits as kame plains. The Newingtot. moraine is reinterpreted as a series of individual kame plains which are not as ideally aligned as earlier indicated. The surfaces of these forms all slope gently southeast in a shingle-like succession with highest elevations to the northwest. The gradual decrease in elevation coastward may be attributed to aggrading ice melt streams

(Tuttle, 1952, p. 64) or to isostatic adjustment of the land in response to unloading by the ice (Goldthwait et al, 1951, p. 44) or to a combination of both processes.

Kettles, locally conspicuous on kame terraces, kame plains, and outwash deposits, are typified by Spruce Hole in Durham, Turtle

Pond in Lee, Hillard Pond in Somersworth, The Hoppers in Dover and

Barrington, Barbadoes Pond in Madbury, and the depressions north of Hampton Center. 7

Blue-gray massive clays dominantly of marine origin overlie the stratified sand and gravel deposits in much of the area, commonly fingering up narrow stream valleys away from the coast*

In a recent study, L* Goldthwait (1953, p. 6) mentions the presence of sand or gravel interbedded with or atop the clays in some sec­ tions* Elevations of the clays are greatest toward the northwest, having been reported at 200 feet in Rochester and at 70 feet in

Rye and Portsmouth by Goldthwait et al (1951, p. 43)*

Marine fossils, both vertebrate and invertebrate, have been cited from similar clays in nearby Maine by Leavitt and Perkins

(1935, p. 204-207).

Inland features once ascribed to marine processes by

J* V* Goldthwait (1925, p. 30-34) were subsequently rejected by him and reassigned to stratified drift.

The present coastline can be classified as compound, showing the combined effects of submergence and glacial modification*

Indicative of submergence are the many and extensive tidal pene­ trations, including Great Bay, which may originally have been several individual branches of the Piscataqua River (Goldthwait et al,

1951, p. 59), numerous islands, spits such as those seen at

Hampton Harbor, and remains of drowned forests at Odiornes Point 8 and Jennesa Beach* Complications brought about by glaciation have permitted development of bars and lagoons now evident at North

Beach and Rye Beach* Boulder pavements, due to the winnowing out of fine material from glacial deposits, are well displayed at the south end of North Beach and around the base of Great Boar's

Head.

Statement of Problem

A detailed study of the bedrock geology of the Dover-Bxeter-

Portsmouth region was undertaken in an attempt to resolve the stratigraphic succession and to determine structural relation­ ships of the metamorphic and igneous rock units. The character of metamorphism within the selected area was an important part of the investigation* GENERAL STRAT1GRAPHIC RELATIONS

General Statement

The stratified rocks of the Dover-Kxeter-Portsmouth region generally strike northeast-southwest and range in age from

Ordovician(?) to Lower Devonian, Billings (1956, pp. 25-35,

38-44), in discussing the stratigraphic units of southeastern

New Hampshire, dates the formations as follows: Rye formation —

Ordovician(?), Kittery quartzite -- Silurlan(?), Eliot formation —

Middle Silurian(?), Berwick formation -- Middle Silurian(?), and

the Littleton formation -- Lower Devonian. Progressively younger rocks occur from southeast to northwest, exclusive of repetition by folding.

Before metamorphism, the rock types present were primarily

sandstones, siItstones, shales, pyroclastics, carbonate-bearing

rocks, and admixtures of these types. No unconformable relation­

ships were detected in the course of field study.

The grade of regional metamorphism ranges from low to high

and bears a direct relationship to areas of granitic and pegmatitic

intrusives. With the exception of a few very local occurrences

of the hornblende-homfels facies of contact metamorphism (Turner

and Verhoogen, 1960, p. 511-520), the metamorphic rocks are in the

greenschist and almandine-amphibolite facies of regional meta­

morphism (Turner and Verhoogen, 1960, pp. 533-541, 544-553).

These last two facies include the more commonly used chlorite,

9 10

biotite, garnet, staurolite, and alllimanlte zones of regional metamorphism. Rocks of the greenschist facies occupy the central

and greatest part of the nap area, with a large area of rocks of

the almandine-amphibolite facies adjacent to the seacoast and a

sonewhat smaller area in the northwest part of the region.

Staurolite occurs only in part of the western band of more highly

metamorphosed rocks and garnet is exceedingly rare in the upper

member of the Rye formation in the east; the absence of these two minerals is probably related to rock compositions incompatible

with their formation.

Metamorphic rocks of southeastern New Hampshire have been

invaded by igneous rock bodies of the Upper Devonian(?) Hillsboro

plutonic series and the Mississlppian(?) White Mountain plutonic

series, which range from syntectonic to post-tectonic relative

to the Acadian orogeny. Most of the igneous bodies are generally

concordant with their host rocks.

Fossil evidence is absent from southeastern New Hampshire and

correlations were made by extending formational boundaries from

the previously mapped Mt* Pawtuckaway quadrangle to the west

(Freedman, 1950). Rye Formation (Ordovician?)

General statement

The Rye formation, as a distinct and separate unit, was first specifically described by Katz (1917, p. 167-168) as an

"Algonkian(7) crystalline complex". DSndke (1922, p. 143-144) named the strata the Rye gneiss for coastal exposures in Rye town­ ship and retained the Precambrian(?) designation. Billings (1952, p. 23-24) described and reclassified the unit as the Rye formation and delineated two distinct members: a lower one consisting predominantly of quartzo-feldspathic schists and an upper metavolcanic member containing metamorphosed mafic and silicic vol canic material and metamorphosed sedimentary rocks.

The oldest stratigraphic unit in the region, the Rye forma­ tion occupies a crudely semi-elliptical area adjacent to the seacoast, forming the core of the Rye anticline. Throughout most of its New Hampshire occurrence, except in New Castle and northern most Rye and Portsmouth, the plunge of this anticline is southwest

In southeastern New Hampshire, the Rye formation is approx­

imately 12 miles long southwest from New Castle to Hampton Falls and four miles wide at the northern limit cf its New Hampshire occurrence. The mapped belt tapers southwest as the core of an anticline plunging southwest. 12

The Rye formation, however, continues northeast and underlies almost all of Gerrish Island, Maine; to the east it comprises most of the Isles of Shoals, which are located approximately six miles east of Portsmouth, New Hampshire (Fowler-Billings, 1959, 51 p.).

North from the northern part of Rye the plunge of the anticline is northeast, indicating that the structure is doubly-plunging*

The contact between the two members of the Rye formation, which is conformable and is abruptly transitional through inter- bedded lithologies of both members, is best seen on the southeastern shore of New Castle. Although outcrops of the Rye formation are large and abundant on the coast, they are less numerous inland, where commonly the metamorphic rocks are bulwarked by ribs of concordant intrusive granitic rocks. Some excellent exposures of the Rye are also present adjacent to streams and tidal inlets and in road cuts.

Bedding is usually well defined by lithologic variations, although the lower member of the Rye formation generally presents a somewhat more massive aspect. Thicknesses of beds range from a fraction of an inch to a few tens of feet. Foliation is expressed by planar orientation of platy and prismatic minerals and is rigorously parallel with the bedding in most exposures. Mica trains, aligned quartzo-feldspathic blebs and streaks, oriented prismatic minerals, minor fold axes, and broad corrugations on foliation planes constitute the linear elements. Medium- to coarse-grained granite and pegmatite pods, lenses, and streaks are very abundant throughout the Rye formation, particularly In the lower member. Most of the observed bodies are concordant, although crosscutting relationships occur locally.

Many camptonlte sills and dikes have also intruded the formation.

Billings (1956, p. 39) estimates the thickness of each member of the Rye formation to be 2,000 feet. He tentatively assigns an Ordovician age to the Rye formation and correlates it with the

Ammonoosuc volcanics of western New Hampshire (p. 104).

Lower metasedimentary member

General statement

The oldest rocks in the area, those of the lower member of the Rye formation, occur in the core of the northeast-southwest trending Rye anticline. Rocks in this member, as indicated by mineral compositions, belong to the almandine-amphibolite facies.

Rock types of the central portion of the anticline, which are assignable to the sillimanite-almandine-muscovite subfacies, are transitional on the west and south to rocks of the kyanite-almandine- muscovlte and staurolite-almandine subfacies. Due to the lack of the indicator minerals kyanite and staurolite, however, the two subfacies could be distinguished by the writer as belonging to the almandine-amphibole facies only by the presence of plagioclase more calcic in composition than An^,. (Turner and Verhoogen, 1960, p. 533). 14

Complicating the analysis of regional metamorphism is the presence of many small granite and pegmatite bodies, which locally contribute a contact metamorphic effect. Minor amounts of silli- rnanite occur at or near the contact of the granitic rock bodies with the host rock in the area of the kyanite-almandine-muscovite and staurolite-almandine subfacies. It is impossible, however, to show these occurrences on the map at the scale used.

Although the lower member of the Rye formation consists of many petrographic varieties, a grouping of the lithologies under the headings of schists, quartzites, and lime-sllicate rocks seems feasible because of their transitional nature and for ease of discussion. Approximate modal analyses for some representative rock types are given in Table 1.

Schists

In this group, the greatest percentage is quartzo-feldspathic

in character, and the most common single rock type is feldspathic quartz-mica schist. With an increase in biotite and muscovite

and a decrease in quartz and feldspar content, there is a transition

to more micaceous schists.

The quartzo-feldspathic schists are tough,medium-grained, light

to medium gray rocks that weather light gray or buff. The more

schistose rock types are darker in color, commonly dark brown or

-black, and weather more rapidly than other schist types. 15

With the exception of silllmanlte-bearing varieties, schists throughout the lower member of the Rye formation are very similar.

The most easily identified mineral types in hand specimen are quartz, feldspar, biotite, muscovite, and garnet. Megascopic

sillimanite was observed only in schists at Odiornes Point, North

Rye, occurring there as fibrous sheaves to 1 cm in length. At

this locality, and for about 0.5 mile to the south, igneous quartzo-feldspathic material forms seams in the host rock so

intimately along bedding and foliation planes that the composite

rock may well be termed a lit-par-lit gneiss.

Microscopically, the essential minerals of the schists are

quartz, plagioclase, biotite, and muscovite. Garnet, sillimanite,

and chlorite are abundant in but few places. Common accessories

include zircon, epidote-zoisite, apatite, tourmaline, sphene, and

iron oxides.

Quartz is the most dominant matrix mineral, occurring in

equigranular interlocking and sutured grains with undulatory

extinction, as partially reconstituted spears in flow-like structures

around feldspar and garnet, and, least commonly, in an equigranular mosaic exhibiting strain shadows.

The quartz spears show fair to good optical orientation within

the plane of foliation, as determined by use of the petrographic microscope and the gypsum plate. Evidence of cataclasis is most

prominent in the northern part of the area and least apparent in 16 rocks to the south. Individual quartz grains range from .005 to

0 . 3 n o in size and generally compose from 27 to 53 percent of the rocks. In the very micaceous varieties, however, the amount may be as low as 5 percent. Included in some quartz are rounded blebs of magnetite and euhedral apatite and tourmaline. The last two minerals are broken in some thin sections, indicating some movement after crystallization.

The dominant feldspar, ranging from 3 to 45 percent by volume, is oligoclase-andesine (An^Q_3 y) and appears as small grains in the matrix and as porphyroclasts as much as 0.6 mm in diameter.

Albite twinning, conspicuous in all thin sections, is bent and distorted and is partly masked, in some specimens, by sericitic alteration. Other evidences of post-crystallization deformation are fractured grains and porphyroclasts of plagioclase and the marginal granulation of feldspar, which has resulted in lens-shaped remnants. Some myrmekitic intergrowth was noted where the plagio­ clase is in contact with microcliae or microcline-microperthite.

Notable inclusions in the feldspar are biotite, muscovite, tourma­ line, apatite, and iron oxides.

Alkalic feldspar is present in very subordinate amount and size and consists principally of anhedral grains of mlcrocline and microcline-microperthite. 17

Biotite, pleochroic in light yellow to deep red-brown, occurs as large bent, distorted, and shredded flakes wrapped around porphyroclasts of feldspar and garnet, around remnant eyes of uncrushed rock, and as oriented small wisps in the quartzo-feldspathic matrix. Sizes range from .18 mm in the wisps to 0.5 cm In the large bent flakes. Some biotite exhibits light yellow to medium green pleochroism and appears to be a retrograde metamorphic product transitional to chlorite. A similar mineralogic occurrence has been reported by-Billings (1937, p. 549).

Poikiloblaatically included in biotite are euhedral to sub- hedral zircon grains with attendant pleochroic haloes, irregular grains of magnetite and hematite, and unidentified acicular inclusions, probably rutile, which are arranged in a stellate pattern in some flakes. Less commonly included are euhedral

tourmaline and apatite and anhedral epidote-zoisite grains. Biotite

is altered to chlorite in some specimens, and to sillimanite in others.

Muscovite, like biotite, is present as fine shreds and

larger distorted flakes. Intergrowths with biotite are common.

Additionally.mascovite occurs as a replacement of sillimanite,

retaining the fibrous habit and transverse fractures of that mineral. 18

Retrogressive chlorite, pleochroic in light to medium green, shows the ultrablue interference colors of penninite. The chlorite is an alteration of biotite and garnet and contains grains of magnetite, hematite, haloed zircon, and an unidentified acicular mineral, probably rutile.

Fractured garnet porphyroblasts and porphyroclasts, probably almandine, are pink in color and isotropic. Most are subhedral to anhedral* The maximum observed size is 2.4 mm. Where granulation is extensive, garnet fragments are somewhat dispersed and the individual particles are slightly anisotropic. Most of the garnet is poikiloblastic, and includes irregular grains of magnetite and hematite and, less abundantly, quartz grains and tiny slivers of biotite. Alteration, which is marginal and along fractures, is to brown and green biotite and to chlorite.

Fibrolitic sillimanite, in bent and twisted bundles, occurs in the more micaceous schists and is associated with biotite, from which it apparently has been derived. Where biotite is the parent material, exsolved grains of iron oxide are present on the margins of the sillimanite. Alteration to muscovite with retention of the

fibrous character of the sillimanite is common. Some rock specimens show individual needles of fibrolite penetrating quartz and plagio- clase. Sizes range from 1.8 mm to 3.8 mm. 19

Rare remnant andalusite shows alteration to sillimanite, muscovite, and sericite, and occurs most commonly in rocks adjacent to granite and pegmatite lntrusives. Inclusions are quartz, biotite, tourmaline, and zircon,

Euhedral tourmaline, colorless to olive in thin section and black in hand specimen, appears in many samples. Sufficient numbers are broken and granulated to indicate that this mineral predates final regional movement* Tourmaline is included in quartz, plagioclase, and biotite.

Accessory magnetite, pyrite, hematite, and limonite constitute only very minor amounts quantitatively. Epidote-zolsite appears as a minor plagioclase alteration. Anhedral zircon and sphene are present in trace amounts.

Approximate modal analyses of some schists of the lower member of the Rye formation are given in Table 1.

Quartzites

Dense, vitreous, thin-bedded to massive, medium to dark gray quartzites, with a faint purplish cast, are interbedded with and are gradational into schistose rock types. A crude foliation is expressed by planar orientation of the micaceous minerals present.

Beds range from a fraction of an inch to a few feet in thickness. 20

Microscopically the quartzites show considerably less cata- clasis than do the schists, although fluxional structure and por- phyroclastic minerals are present to a limited degree. Quartz is the dominant mineral with plagioclase, biotite, muscovite, garnet, and chlorite present in lesser amounts. Minor accessory minerals are zircon, apatite, tourmaline, epidote, clinozoisite, magnetite, hematite, limonite, and calcite.

Quartz appears as sutured and strained grains with some flux- ional structure around porphyroclasts of plagioclase, garnet, and remnants of uncrushed rock. Less comnonly quartz is equigranular and granoblastic and is present in this habit in the southern­ most exposures of the lower member of the Rye formation. Grain sizes range from 0.005 mm to 0.6 mm.

The plagioclase of the quartzite, which comprises from 11 to

38 percent of the rock, is oligoclase (A^o-lS^ * Both albite and

Carlsbad twinning are present. Most plagioclase is slightly sericitized and shows evidence of deformation by the presence of fractures and bent twin lamellae. More pronounced effects are marginal granulation and the dispersal of fragments; the residual porphyroclasts are contained in a finer quartzo-feldspathic matrix.

Myrmekitic margins on plagioclase are rare. Only quartz, biotite, and apatite are poikiloblastic in the plagioclase.

Microcline-microperthite appears rarely as disseminated grains in the matrix and contains the same minerals listed for plagioclase. 21

Oriented biotite, which makes up as much as 9 percent of the rock, occurs as widely distributed visps and as larger porphyro- blasts in the more micaceous quartzlte beds. Sizes are from 0.285mm to 2.4 mm. in the more deformed beds, the pleochroism of biotite is light yellow-green to medium green, which suggests that this variety of biotite is a product of retrograde metamorphism or hydrothermal activity, and is transitional between the more comnon type of biotite and chlorite, Comnon inclusions are euhedral to subhedral zircon grains with pleochroic haloes and irregular grains of magnetite and hematite, which also border some of the more distorted flakes of biotite as products of exsolution.

Chlorite occurs in minor quantity as an alteration of biotite and is pleochroic from light yellow to medium green. Interference colors of ultrablue indicate a penninitlc chlorite. Because of its association with minerals of higher metamorphic grade, the chlorite is regarded as retrogressive in origin.

Almandlne garnet appears in several thin sections as fractured euhedral to subhedral porphyroblasts and as irregular and angular grains, slightly dispersed but aligned, which suggest derivation from originally larger units. The maximum size observed was 2.10 mm.

In a few specimens muscovite occurs both as large bent blades and as fine shreds. Intergrowth with biotite is common. Snail grains and clusters of epidote-zoisite are associated with biotite and chlorite and with plagioclase as an alteration product. Euhedral to subhedral zircon characteristically Is

Included In biotite, feldspar, and quartz. Tourmaline, colorless to olive In pleochrolsm, occurs as snail euhedra in quartz, feldspar, biotite, and muscovite. Euhedral apatite is Included in quartz and feldspar. Magnetite, hematite, and llmonlte, as irregular grains, are present in biotite, chlorite, and muscovite.

Amphibolites

A few beds and elongate lenses of coarse-grained amphibolite are Interbedded with and are gradational into schist types previously described. Individual beds average 0.5 to 5 inches in thickness. Good exposures are located on the Rye coast 0.25 mile west of Frost Point and on Mill Road, 1 mile south of the Rye-

North Hampton town line.

The dark green amphibolite, which weathers a lighter green,

shows megascopic dark green amphibole, pink garnet, and, less commonly, dark brown biotite. Schlstosity along the margins of amphibolite bodies is expressed by the parallelism of amphibole and, where present, biotite flakes. 23

In thin section the rocks are grauoblastic, grading to schistose toward the contact with other lithologic types* Quartz grains, equigranular in form, exhibit strain shadows in all samples examined. The percentage of quartz ranges from 3 to 32.

The plagioclase is labradorite (^**54^55), which shows the effects of strain in bent albite twin lamellae. Plagioclase poikiloblastically encloses quartz grains. Sericitic alteration, though minor, is ubiquitous. Microcline occurs in only trace amount.

Hornblende, which is pleochroic from light yellow-green to green, occurs as euhedral porphyroblasts enclosing quartz, feldspar, magnetite, sphene, and hematite. Minor marginal alter­ ation to biotite in some specimens is probably a result of potash introduction from adjacent granitic masses. Quantitatively hornblende comprises as much as 43 percent of the rock.

Colorless diopside comprises a maximum of 46 percent of some amphibolites and occurs both as individual grains and as cores of hornblende.

Biotite is conspicuous in both the transition zone to other rock types and within the amphibolite itself as an alteration.

It is pleochroic from light yellow to light red-brown.

Irregular grains of sphene containing magnetite cores and blebs of epidote-zoisite are associated with the amphibole.

Apatite and zircon euhedra are present in quartz, feldspar, and amphibole. Magnetite is the principal opaque mineral. 24

According to Heinrich (1956, p. 255-256), amphibolites of intrusive igneous origin might be expected to show at least one of the following characteristics: 1) normally zoned plagioclase;

2 ) relict igneous structure; 3) remnant augite or hypersthene; or

4) crosscutting relationships with the host metasedimentary rocks.

None of these criteria pertains to amphibolites of the lower member of the Rye formation, hence it is tentatively concluded that the amphibolites are probably of tuffaceous origin, perhaps contaminated in part by sedimentary material which was being deposited concomi­ tantly.

Although an impure carbonate origin for most of the am­ phibolites cannot be completely dismissed, the absence of marble

lenses and beds and other carbonate-rich rock types in the lower member of the Rye formation increases the probability of a pyroclastic origin for most of the amphibolites. The presence of diopside in

some amphibolites, however, suggests the possibility of a sedimentary

origin for some of these rocks. 25

Upper metavolcanic member

Generel statement

This unit appears on the map as a single band peripheral to the

lower member of the Rye formation in the Rye anticline. Outcrops

in the area of contact of the two members on the southeast coast of

New Castle reveal a conformable and gradational relationship. The

contact of the metavolcanic member with the younger Kittery formation

to the west, on the other hand, is in part conformable, as deduced

from structural data in the south of the map area, and in part a

fault contact in the northern area. The actual contact is nowhere

exposed.

Rocks of the upper member probably lie within the kyanite~

almandine-muscovite subfacies and staurolite-almandine subfacies

of the almandine-amphibollte facies of regional metamorphism.

The presence of plagioclase of composition An^-An^g indicates rocks

of higher grade than the greenschist facies (Turner and Verhoogen,

1960, p. 533), but the indicator minerals staurolite and kyanite

are lacking and garnet is sparsely distributed, hence a strict

delineation of the subfacies is not generally possible.

Representative modes of rock types of this unit are given in

Table 2. 26

Amphibolite, hornblende schist, and quartz-biotite-plagioclase gneiss, which are considered to be metavolcanic rocks by Billings

(1956, p. 39), occur in sufficient abundance to characterize the

upper member of the Rye formation. However, metasediments are

approximately equal, quantitatively, to the metavolcanics. Of

the many metamorphosed sedimentary rock types present, those most

common to the upper member are finely interlaminated feldspathic

quartz-biotite schists and feldspathic quartz-actinolite schist,

biotite schist, and garnetlferous quartzite. An injection and

permeation gneiss, which is locally conspicuous, involves elements

of both the metavolcanic and metasedimentary rocks of the upper member of the Rye formation.

Metavolcanic rocks

Amphibolites and hornblende schists occur in elongate lenses

and beds to 20 feet in thickness interlayered with and transitional

into metasediments. They are dark green to black, but weather

to dark gray-green, with the amphibole etched into relief. These

rocks are fine to medium grained and massive to moderately well

foliated. Increase in the size of amphibole and in the degree of

foliation is most apparent adjacent to intrusive materials. 27

Individual beds range in thickness from an inch to 15 feet and are interbedded with the more conmon metasedimentary types*

Lineation is vaguely expressed by a subparallel to parallel orientation of hornblende and more distinctly by coarse grooves on bedding-foliation planes and by minor fold axes*

Megascopically the minerals are chiefly amphibole and feldspar*

The amphibole generally occurs in poorly to well oriented dark- green to black needles averaging from less than 1.0 mm to 1.75 mm long. Rarely do they attain a length of 6.0 ms. Feldspar most commonly takes the form of white to light-green blebs with a maximum length of 3 mm. Biotite is locally developed adjacent to intrusives of granitic composition. Thread-like veinlets of epidote and chlorite, with some minor quartz and albite, are present in most outcrops; these minerals probably formed by hydrothermal activity from acidic intrusives.

No relict textures or structures indicative of the volcanic origin of these rocks have been identified in either the field or laboratory, but the degree and type of metamorphism would tend to obliterate such evidence. A few of the amphibolites may be metamorphosed basic sills, however, according to the criteria set forth by Heinrich (1956, p. 255-256). 28

Under the microscope, mineral granulation testifies to post­ recrystallization movement. The amphibole is present as euhedral prisms and as shredded and streamlined porphyroclasts. Alter­

ation products are epidote-zoisite, chlorite, and, proximal Co

granitic intrusions, biotite.

Plagioclase, ranging from calcic oligoclase to calcic

andesine (^25-48^ » exhibits both albite and Carlsbad twinning.

Bent and fractured grains and marginal granulation producing augen

forms are evidence of cataclasis. Sericitization is present in

all specimens, ranging in degree from slight to moderate.

Epidote, clinozoisite, and carbonate are additional alteration

products.

Prominent among the accessory minerals is sphene with

magnetite cores. Anhedra of sphene occur in the matrix and as

inclusions in plagioclase and hornblende. Magnetite blebs are

present in sphene, amphibole, and biotite. Grains of epidote-

zoisite are marginal alterations of plagioclase and hornblende.

Fibrous light-green chlorite with ultrablue interference colors,

probably penninite, constitutes a minor derivative of hornblende.

Euhedral apatite and zircon are present in hornblende, plagio­

clase, biotite, or chlorite in trace amounts in all thin sections.

Pleochroic haloes surround the zircon grains in hornblende, biotite,

and chlorite. Hematite and tourmaline are very minor accessories. 29

Hornblende schists differ from the amphibolites primarily in greater degree of foliation, in higher percentage of biotite, and in the presence of appreciable amounts of quartz* These schists are intermediate between amphibolite and nonvolcanlc metasediment.

The amphibole-rich rocks suggest that the parent material was a tuff of andesitic or basaltic composition, and those rocks containing appreciable quartz may represent rocks of mixed vol­ canic and sedimentary origin.

The metamorphosed mafic volcanic rocks are well exposed in the Beverly Hill quarry, Portsmouth, 0.5 mile southwest of Lafayette

Road.

Quartz-biotite-plagioclase gneiss, in beds to 100 feet in thickness, are interbedded with other lithologlc types of the unit.

The gneiss is generally a dark gray, medium- to coarse-grained, moderately well foliated rock with conspicuous porphyroblasts of white plagioclase and dark-brown to black biotite. Veathered surfaces are medium to light gray with chalky strips of quartzo- feldspathic material etched into relief. Foliation, lineation, and cataclasis are most prominent at or near intrusive contacts where granitic injections 1/8 inch to 1/2 inch wide are common, tfhat appears to be relict hornfelsic texture is present where

intrusives are least numerous. 30

Where contacts of the gneiss with other lithologic types of the member are exposed, they are gradational. There is no system* atic or mappable distribution of the gneiss, which occurs randomly

in the upper member of the Rye formation.

Microscopically, quartz, plagioclase, and biotite are the

essential minerals. Quartz grains show effects of deformation

in varying degree ranging from undulatory extinction to finely

recrystallized grains in spears oriented physically and optically

in the plane of foliation. Sutured boundaries are the rule,

although some hornfelsic mosaic patterns are present. As much

as 45 percent quartz was observed in the gneiss.

Sodic oligoclase occurs as porphyroblasts with

marginal granulation and bent and broken twin lamellae and com*

prises as much as 35 percent of the rock. Common poikiloblaatic

inclusions are quartz and biotite. Sericite and epidote are

conspicuous alterations of the plagioclase. Only very minor

amounts of microcline-microperthite are normally present in the

rock, although the percentage is increased perceptibly where the

gneiss is in contact with granitic Intrusives and injections.

Myrmekite, which is rare, fringes grains of oligoclase.

Bent and shredded biotite flakes are of two distinguishable

types. One, the more common, is pleochroic in light yellow-

brown and dark brown; the other type, pleochroic in light brownish

green and green, appears to be intermediate between the brown biotite and true chlorite, owing its presence to alteration of biotite by retrograde metamorphism or by hydrothermal activity.

In the second variety of biotite are stellate patterns of acicular inclusions, possibly rutile. Pleochroic haloes about zircon grains are present in both types of biotite. Additionally included in biotite are anhedral epidote-zoisite grains. As much as 25 percent biotite was observed in the gneiss.

Chlorite, pleochroic in light green and gray-green and showing ultrablue interference colors, is the common alteration of biotite. Muscovite, in trace quantity, exists as elongate flakes intergrown with biotite. Sericite is a plagioclase alteration present in all thin sections.

Euhedral apatite grains, occurring in quartz and feldspar, are broken and dissociated in some thin sections. Euhedral zircons occur in feldspar, biotite, chlorite, and muscovite, surrounded by pleochroic haloes in biotite and chlorite. Formless grains of epidote-zoisite occur as minor plagioclase alterations. Calcite

is a very minor alteration of the same mineral. The few irregular masses of sphene present have magnetite cores.

Almandine garnet, which is very sparsely distributed in the gneiss, ranges from euhedral dodecahedra to irregular clots.

Fracturing of the garnet with some dispersal of fragments is common, as is a minor amount of chloritic alteration marginally and along

fractures. 32

Pyrlte, magnetite, and llmonite are the principal ore minerals and they are associated primarily with biotite and chlorite, although some grains are inclusions in quartz and feldspar or occupy the cores of sphene masses*

The origin of the gneiss is problematical. It may represent a metamorphosed dacitic tuff similar to that described by Chapman

(1939, p. 133) from the Ordovician Orfordvllle formation in the

Hascoma quadrangle* However, the lack of relict llthic fragments and cross-cutting relationships necessitates an original fine­ grained, perhaps water-laid, tuff. An arkosic sediment has been considered as a possible source for the gneiss, but gradational contacts with granitic and pegmatitic rocks in many outcrops, particularly in those where the igneous materials are patchy and grossly transgress lithologic boundaries but retain the schistosity of the gneiss, suggest a permeation or injection origin for the gneiss. Additionally, the composition of the gneiss generally agrees with that of the injection and permeation gneiss discussed below.

No exposures of the quartz-biotite-plagioclase gneiss were found in North Hampton township. This may be accounted for by the lack of original deposition of volcanic tuff or arkose or by the lack of uplift and exposure of pelitic or seml-pelitlc rocks invaded at depth by granitic or pegmatitic material. 33

Particularly good exposures of the quartz-biotite-plagioclase gneiss are located on the northeast-trending bedrock knob at the intersection of Lafayette Road and Sagamore Creek in Portsmouth and on the south-central coast of New Castle.

Metasedlmentary rocks

Particularly characteristic and most abundant in this group of rocks are tough finely interbedded maroon or brown feldspathic quartz-biotite schists and light-green to light gray-green felds­ pathic quartz-actinolite schists. Although each of these types occurs singly in greater thicknesses, most exposures show per­ sistent individual bands 1/16 inch to 3/4 inch in thickness.

There is no significant color change due to weathering, but differential resistance has resulted in corrugations or ribs of the amphibole-bearing laminae. Transition between the two litho- logic types is megascopically abrupt.

Grain size varies from very fine to fine, with foliation expressed by the planar orientation of minor amounts of biotite and actinolite. Minor folds are well displayed in these rocks and

range in amplitude from less than an inch to several feet. The

abandoned quarry 0.75 mile southwest of the bridge to New Castle

in Portsmouth contains many fine examples of folds as well as the

lineations demonstrated by broad corrugations on bedding surfaces and by minor fold axes. 34

la a few localities» metamorphism by granitic intrusions has produced a coarser grain size, particularly of the biotite and actinolite. Biotite, ordinarily less than 1.15 mm, attains

sizes of greater than 1.50 mm, and actinolite exceeds 3.0 mm, in contrast to a more common dimension of 1.50 mm or less. In only a few isolated instances do intrusives penetrate these laminated rock types; rather, the granites occur at the contacts with other

rocks in the member. This exclusion may be attributable to the

density and toughness of the laminae.

Microscopically the transitional nature of the two laminated metasedimentary rock types is clearly shown by a zone that contains

both biotite and actinolite. Granulation in these rocks is greatest

at contacts with other lithologic types, with the effect diminish­

ing away from contacts until, in some cases, a hornfelsic texture

is dominant.

The essential minerals of the feldspathic quartz-actinolite

schist are quartz, plagioclase, and actinolite. The quartz

grains vary from angular to subangular or sutured, depending on

the degree of cataclasls and recrystallization. Fluxional spears

of finely comminuted and slightly reconstituted quartz are present

in some places in these rocks, as in others previously described. 35

The plagioclase, calcic oligoclase to andesine (^28-47^ * exhibits albite twinning and, to a lesser degree, Carlsbad twinning.

In rock samples showing little cataclasis, the feldspar is an integral part of the more or less equigranular matrix in which actinolite occurs as porphyroblasts. In the deformed rocks, however, the plagioclase survives as streamlined fractured and bent porphyroclasts in a fine-grained matrix. In all instances, sericite is the dominant alteration product; calcite, epidote, and clinozoisite are minor derivatives.

In appearance, the amphibole varies from euhedral grains to fractured, shredded, and lens-shaped porphyroclasts. Poikilo- blastically included are grains of quartz, plagioclase, zircon, and sphene. Epidote and clinozoisite are minor alterations.

A trace of colorless diopside is present with the amphibole in rocks adjacent to some granitic intrusives.

Sphene, both euhedral and anhedral, most commonly has magnet­

ite cores. Minute apatite crystals are present in quartz and plagio­

clase. Magnetite blebs are randomly disseminated in the rock,

as are lesser amounts of cubic pyrite, and hematite pseudomorphs

after pyrite; limonite appears as stain and irregular blotches.

Euhedral tourmaline, containing quartz and feldspar, occurs

sparsely in proximity to granitic bodies. 36

The feldspathic quartz-biotite schist contains quartz, plagio­ clase » and biotite as essential minerals; minor constituents are chlorite, epidote, clinozoisite, sphene, apatite, zircon, calcite, and magnetite. Textural and structural characteristics of the rock are identical to those of the feldspathic quartz-actinolite schist.

Quartz appears microscopically as elongate, partially recrystallized lenses where cataclasis has been strongest, and as equant and sutured grains in hornfelsic occurrences. Plagioclase, an andesine ranging from A n ^ to An^, shows varying degrees of deformation from bent albite twin lamellae to augen-shaped porphyroclasts. A low index feldspar (albite?) fills fractures in the andesine. Slight to moderate sericitization is ubiquitous.

Biotite occurs as bent flakes and shreds differing but little in size from the associated minerals save near granitic intrusives where flakes attain a maximum of 6.35 mm. Elsewhere the average size is less than 0.80 mm. The biotite is pleochroic from light yellow to light orange-brown. Poikiloblastically Included are epidote, clinozoisite, sphene, magnetite, and haloed zircon.

Colorless to light-green penninitic chlorite with ultrablue inter­ ference colors is present as a minor alteration of biotite. 37

Epidote and clinozoisite exist as random grains and as a very minor alteration of plagioclase. Small amounts of euhedral to anhedral sphene are also present. Minute apatite crystals are contained in quartz and feldspar. Zircon and magnetite are most commonly present in biotite, although both are generally dis­ seminated throughout the rock in small quantities. Calcite is a very minor alteration product of plagioclase.

Black biotite schist, quantitatively comprising but a small percentage of this member of the Rye formation, is significant in that it acts as a host in the formation of an injection gneiss.

Almost invariably where the schist is found, the gneiss is present.

Field relationships indicate that this biotite schist is tran­ sitional to feldspathic quartz-biotite schist in most places, although in a few places it grades into the quartz-biotite-plagioclase gneiss.

Under the microscope, essential minerals are biotite, quartz, and feldspar. The biotite is pleochroic from light yellow to orange-brown and is bent and torn. Poikiloblastically it contains magnetite, hematite, zircon, and epidote. Alteration is to a penninitic chlorite. Quartz is distorted and granulated, as in other lithologic types in the member. Oligoclase (Ani5 „i7 ) the sole feldspar and is moderately sericitized. Garnet as much as

1.30 mm across occurs in some specimens. Accessory minerals are epidote, clinozoisite, magnetite, pyrite, hematite, zircon, apatite, and tourmaline. Injection and permeation gneiss

Unique to the upper member of the Rye formation is an injection and permeation gneiss consisting of an igneous quartzo-feldspathic component in a host of biotite schist, amphib­ olite, or hornblende schist. The rock presents an appearance of black matrix with light gray or white porphyroblasts and augen of plagioclase. Schistosity varies from moderate to strong in develop­ ment, depending on the relative proportion of host rock and the location in respect to contact with other lithologic types, particularly those of intrusive igneous origin. Foliation parallels lithologic contacts generally.

The conspicuous feldspars are euhedral to augen in form and range from 1.6 mm to 10.2 cm in length, as shown in Plates II and

III. In thin units of gneiss and near contacts, the augen shape is dominant, although centrally, in broader bands of gneiss, the euhedral feldspar is conspicuous. Barbour (1930, p. 356) suggested that if the host rock had sufficient plasticity, idiomorphic forms

V might develop in an injected rock mass. Concomitant or subsequent shearing, however, could produce smaller and more lenticular porphyroblasts (porphyroclasts) at or near lithologic contacts. 39

PIATE II

Outcrop of permeation and injection gneiss in the upper member of the Rye formation showing relict bedding. Foliated feldspathic gneiss with interbeds of lime-silicate rock. Light-colored blebs are oligoclase. Light-colored wedge is quartzo-feldspathic material.

Scale is shown by the half dollar. Fort Constitution, northeastern

New Castle, New Hampshire, 40

PLATE III

Outcrop of permeation and injection gneiss in the upper member of the Rye formation showing large feldspar augen. Oligo- clase augen and quartzo-feldspathic streaks in foliated gneiss.

Fort Constitution, northeastern New Castle, New Hampshire.

* 41

Recognition of the injection and permeation gneiss, as such,

Is extremely difficult in the field and only a compilation of data from megascopic and microscopic study provides sufficient evidence to support this hypothesis of origin. These data are as follows:

1. The common host rock, biotite schist, in some places

garnetiferous, has been observed to grade into identifiable

metasediments of more quartzose nature.

2. Where the transition to a less schistose rock occurs,

the feldspars are smaller in size and less in quantity,

suggesting that the gneiss exists because of the presence

of a permissive rock type.

3. Although biotite schist is the predominant host for the

injections, a similar gneiss is developed in amphibolitic

rocks, exhibiting characteristics similar to those

mentioned above and also containing oligoclase, in

contrast to the more common andesine of amphibolites.

4. Weathering of some outcrops has etched into relief the

igneous quartzo-feldspathic component, demonstrating

the otherwise not too evident continuous nature of the

material.

3. Under the microscope, both biotite and hornblende are

included in the feldspars, intimating a late stage of

feldspar formation. 6. Unoriented needles and fragments of sillimanite, which

are also contained in a few feldspar porphyroclasts,

suggest a sedimentary origin for part of the gneiss.

This evidence agrees in part with Ch'ih (1950, p. 94),

who observed relict garnet, kyanite, sillimanite, and

biotite in granitized rock in the Wissahickon schist

near Philadelphia, Pennsylvania.

7. The quartz strips attributed to injection of igneous

material are microscopically remarkably free of con­

tamination and possess the mosaic texture of igneous

quartz.

8. Veinlets and thin sill-like bodies comparable in texture

and composition to the proposed added component occur in

other foliated rock types in this member of the Rye

formation.

Microscopically, evidence for deformation is present in all thin sections. Intensity of deformation varies from bent feldspar twin lamellae and simple strain in quartz to augen feldspars and finely granulated streaks of quartz.

As in rocks previously described, quartz is fine grained and in streaks, except for those injections which suffered the minimum cataclasis. Here the size of grains is somewhat larger and no optical orientation of individuals is apparent. 43

Laths and augen of feldspar are primarily ollgoclase (An^Q.^^) in all variations of the injection gneiss, Including those derived from amphibolite. This is similar to the finding of Read (1931, p. 120-121) who studied augen gneisses developed in pelitic and semipelitic rocks. Twinning is of the albite type, for the most part, although some Carlsbad forms were observed. Sericitization ranges from moderate to intense, tthere fractures in ollgoclase have been healed, the components involved are primarily quartz and microperthite; to a lesser degree the seams consist of carbonate.

Biotite, as much as 9.52 mm in diameter, conforms to the contours of the injections though in some places it penetrates and is included totally in ollgoclase. Host biotite is pleochroic in light brown and red-brown, but a minor amount is pleochroic in olive-green to dark brown. Chlorite is the sole alteration derivative of biotite.

Muscovite appears but rarely and is associated and intergrown with biotite. Chlorite, var. pennlnite, is an alteration of biotite and garnet.

The few garnets present are in the schistose host rock and poikiloblastically include quartz and magnetite. Invariably the garnet is anhedral, fractured, slightly dispersed, and altered to

chlorite peripherally and along fractures. 44

Euhedral to anhedral magnetite is generally disseminated throughout the rock and is altered to hematite in some specimens.

Epldote and cilnozoisite anhedra appear in biotite and as an alter­ ation of plagioclaae. Other accessory minerals are zircon, apatite, sphene, and carbonate.

A photomicrograph of the injection and permeation gneiss is shown in Plate IV.

Excellent exposures of the quartz-biotite-oligoclase injection and permeation gneiss occur along the southeast margin of Sagamore

Creek near the junction of Routes 1A and IB in Portsmouth, labeled on the maps as Electric Railroad and Wentworth Road.

Injection gneiss formed by addition of quartzo-feldspathic material to amphibolite or amphibole schist differs little in its general characteristics from the variety already described.

Hornblende, as much as 3.17 mm in length, occurs typically in porphyroclastic habit. Its optical properties are identical to the amphibole of the uncontaminated basic metavolcanic rocks.

Alteration to biotite and chlorite is evident in all thin sections, the former mineral suggesting the addition of potash from the igneous component of the gneiss.

The major feldspar is oligoclase wblcb contains amphibole, biotite, chlorite, quartz, epidote, and clinozoisite.

In form, the plagioclase varies from euhedral laths to augen.

Fractures are healed by raicrocline-microperthite. 45

PLATE IV

Photomicrograph of permeation and Injection gneiss in the upper member of the Rye formation. Light-colored fractured and

faulted mineral is oligoclase (ol); dark patches and shreds are

biotite (b). Fine-grained groundmass is quartz, oligoclase, and

sericite. Fort Constitution, northeastern New Castle, New

Hampshire. (Plane polarized light.) 46

Biotite, pleochroic in light orange to dark brown, is present as an alteration of amphibole. Some specimens, however, show a pleochroism of light yellow-green to dark brown-green. Chlorite has developed from amphibole and biotite.

Accessory minerals are apatite, included in quartz and feldspar; sphene with magnetite cores included in amphibole; epidote and clinozoisite as alterations of plagioclase and amphibole; zircon and carbonate.

Excellent exposures of the quartz-hornblende-oligoclase injection and permeation gneiss occur on the foot-like extension on the southwest part of New Castle.

Kittery Formation (Silurian?)

General statement

The Kittery formation was originally named the Kittery quartzite, of Carboniferous age, by Katz (1917, p. 168), for exposures

of the unit in Kittery township, Maine, which lies across the

Piscataqua River from Portsmouth, New Hampshire, and which he estimated to be 1,500 feet in thickness. Because of a paucity of

beds of quartzite and a volumetric predominance of other lithologic

types, however, the writer suggests that the designation Kittery

formation be used. 47

The Kittery formation was probably included in the Merrimack group of C. H. Hitchcock (1870, p. 34) together with strata very similar to those of the Eliot and Berwick formations, which will be discussed below. Billings (1955 and 1956, p. 43) indicated a

Silurian(?) age for the Kittery formation; rocks south of 43° latitude in southeastern New Hampshire he assigned to the Merrimack group, on the basis of geologic reconnaissance. The writer, however, by detailed mapping in the townships of Hampton and Seabrook, has recognized the Kittery formation in outcrops almost to the contact with the Newburyport quartz diorite. Additionally, in the south­ east corner of New Hampshire, there are inclusions in the Newbury­ port quartz diorite and its related porphyritic quartz monzonite which megascopically and microscopically are similar to rocks of

* the Kittery formation.

Four areas of Kittery formation have been mapped. The largest belt of these rocks is 15 miles long in a southwest direction from Portsmouth to Seabrook and has a maximum width of

3.5 miles in the vicinity of Portsmouch. A second extensive body of Kittery formation has been mapped southwest from 1.5 miles east

of Dover, near the Cocheco River, to about one mile south of

Exeter. Two smaller occurrences of the Kittery formation are

located on the western margin of the Exeter quartz diorite pluton, 48 one situated in the southern part of Dover, approximately 2*75 miles long, the other straddling the Newfields-Exeter town line and approximately 1.5 miles long.

The contact of the Kittery formation with the underlying Rye formation is considered to be in part a fault contact and in part a conformable one. The Kittery formation is transitional to the younger Eliot formation through interbedded lithologic types of the two units. Inasmuch as the transition apparently occupies a rather broad area, the map contact, which must be somewhat arbitrarily drawn, is based on the predominance of strata characteristic of either the Kittery or Eliot formations.

Rocks of the Kittery formation are shales, siltstones, impure sandstones, and Impure carbonate-bearing rocks, which have been metamorphosed to slates, phyllites, schists, impure quartzites, and lime-silicate rocks. The two narrow segments of the Kittery formation on the west of the Exeter diorite and the large area adjacent to the Exeter pluton on the east, which flank the

Exeter anticline, belong to the quartz-albite-muscovite-chlorite metamorphic subfacies of the greenschist facies. Local exceptions occur at Fox Point, Newington, on the east shore of Great Bay, and at the contact of the Kittery formation with the intrusive

Exeter diorite. In those places rocks contain biotite and albite and belong to the quartz-albite-epidote-bictite subfacies. 49

The easternmost belt of Kittery formation, which flanks the

Rye anticline on the west and south, includes rocks of the quartz-albite-muscovite-chlorite subfacies, the quartz-albite- epidote-biotite subfacies, and the quartz-albite-epidote-almandine subfacies of the greenschist facies and of the staurolite-almandine subfacies of the almandine-amphibolite facies* In this area of

Kittery formation, the metamorphic grade increases from west to east. Although garnet is exceedingly rare and staurolite absent, the presence of oligoclase, biotite, and chlorite permit facies subdivision of the metamorphic rocks of the Kittery formation.

Rocks of the Kittery formation, near or at the fault contact with the Rye formation, are faulted, sheared, and brecciated.

Two minor fault surfaces, highly stained by limonite, are located at the contact on Lafayette Road, U. S. Route 1, in Portsmouth.

Both faults reflect the relative movements of the major fault zone, in the writer's opinion. Brecciated and partly silicified Kittery

formation crops out 0.4 mile east of Brumble Hill, North Hampton, very near or in the postulated fault zone.

In addition to the localities mentioned above, other excellent exposures of the Kittery formation can be seen on Nobles Island,

Portsmouth, on the hill 0.25 mile west of Woodbury School, Portsmouth,

and on Fox Point, Newington, on the shore of Great Bay. A typical

outcrop of Kittery formation is shown in Plate V. 50

PLATE V

Outcrop of crinkled Kittery formation. Alternating darker biotitic and lighter actinolltic beds. One mile south of Greenland,

New Hampshire. 51

Billings (1956, p. 43-44) tentatively assigned the Kittery formation to the Silurian(?) and estimated its thickness to be

16,500 feet.

Because of the great variety of lithologic types in the

Kittery formation and for ease of discussion, rocks of the unit are taken up under the major subdivisions of slates, phyllites, quartzites, schists, and lime-silicate rocks. Approximate modal analyses of some representative samples of the Kittery formation are given in Table 3.

Slates

In the lowest metamorphic grade of the Kittery formation, dark gray slates, which weather to light or medium gray-brown, are interbedded with the more quartzose rock types. Slaty cleavage of 1/32 inch to 1/16 inch spacing is common and, in most outcrops, intersects bedding at high angles. Slate surfaces are generally lustrous with very fine-grained sericite, and stained blotchily with limonite. Beds of slate, up to 2lj feet in thickness, show no internal bedding.

Microscopically, essential minerals of the slates are quartz, chlorite, and sericite. Quartz, which comprises as much as 41 percent of the rock, occurs as subangular to angular detrital grains and as recrystallized aggregates to .018 mm in size. 52

Quartz veins and lenses parallel and crosscut bedding and cleavage. Chlorite, Identified tentatively as penninlte and prochlorite, makes up as much as 53 percent of some slates and occurs as fine oriented wisps with quartz and sericite. In a few specimens, chlorite Is secondary after biotite. Chlorite Is also present in veinlets, fractures, and on shear planes.

Oriented sericite shreds and wisps constitute as much as 23 percent of some slates.

Of the accessory minerals, plagioclase feldspar, albite of composition Any.iQ, constitutes as much as 12 percent of the slates. Some of the subhedral to anhedral grains of albite are detrital, some metamorphic in origin. Albite twinning is generally bent and the grain margins slightly granulated. Calcite and, in some specimens, dolomite occur as irregular interstitial masses.

Anhedral grains of epidote-zoisite are distributed throughout the rock. In a few specimens, minor amounts of biotite, partly altered to chlorite and pleochroic in yellow to light brown, are intermingled with sericite and chlorite. Pyrite anhedra, partly altered to limonite, are common in all thin sections. Irregular grains of zircon are contained in quartz grains and in chlorite and biotite, with surrounding pleochroic haloes. 53

Phyllites

PhyHites, like the slates, occur primarily in the quartz- albite-muscovite-chlorite subfacies of the greenschist facies part of the Kittery formation. Rocks of this category are crinkled and folded and range from dark gray-green to silvery gray in color.

In hand specimen, pyrite grains and very fine chlorite and sericite are recognizable. Limonite, apparently due to the breakdown of pyrite, stains many outcrops. Laminae, ranging from paper thin to

\ inch, are common. Host exposures show cleavage planes at a high angle to the bedding of the phyllites, and minute faulting of bedding planes.

Under the microscope, the essential minerals of the phyllites

are quartz and sericite. Angular grains of quartz, ranging

from .008 mm to .042 mm, comprise as much as 38 percent of the

rocks. Fine oriented sericite flakes are commonly concentrated

in bands, in addition to shreds disseminated throughout the rock.

A maximum of 71 percent sericite was observed in thin section.

Of the accessory minerals, chlorite occurs as fine flakes

interspersed with sericite and quartz. Ultrablue interference

colors suggest a penninitic variety. Angular fragments of

plagioclase, perhaps detrital, show albite twinning, but are

sufficiently sericitized to prohibit determination of composition. 54

Minor accessories include irregular masses of calcite, dolomite, pyrite that is partly altered to hematite and limonite, euhedral apatite in quartz, anhedral zircon and rutile, and sub- hedral grains of tourmaline.

Schists

Schists constitute the most abundant single rock type in

the Kittery formation, especially in the areas of rock rich in

biotite. In outcrop the schists are fine to medium grained,

finely laminated to massive, and crudely to well foliated.

Laminae range from 1/64 inch to % inch in thickness, and differ

primarily in the relative percentage of biotite. Most of the

schistose rocks are medium gray to dark gray or black, with a

distinct purplish cast. Weathering is to olive or rusty brown.

Nearly all exposures of schist have ramifying veinlets of quartz

which parallel or crosscut foliation. Crystalline calcite coatings

on fracture surfaces are common.

Megascopically identifiable in the schists are red-brown

biotite flakes to 3/4 mm in diameter, some of which are athwart

bedding and foliation, granular quartz, dark-green actinolite

needles to 3 nm long, and muscovite plates to % mm across. 55

Although many varieties of schist occur in the Kittery formation, the most common are biotite-sericite schist, biotite schist, calcareous biotite schist, and biotite-actinolite schist*

The biotite-actinolite schists are, for the most part, tran­ sitional between biotite schists and lime-silicate rocks, exhi­ biting mineralogic and textural characteristics of both.

Microscopically the essential minerals of the various schist types are quartz, biotite, and sericite. Quartz grains, angular to subangular, in part detrital and in part metamorphic, commonly show undulatory extinction. Grains range from granular to sutured and interlocking. Sizes range from .018 mm to

.165 mm. A maximum of about 54 percent was observed in some specimens.

Biotite occurs both as fine interstitial aligned wisps and as random poikiloblastic porphyroblasts, randomly situated, which include anhedral grains of quartz and zircon, the latter with surrounding haloes. Pleochroism of biotite is light yellow to dark red-brown. Porphyroblasts as much as 3/4 mm long were observed. Near the fault contact of the Kittery formation with the

Rye formation, flakes of biotite are distorted and torn. Biotite comprises as much as 49 percent of the schists.

The occurrence of unoriented and undefonned biotite porphyroblasts suggests that the process of recrystallization outlasted the period of regional deformation. 56

Slivers of sericite constitute as much as 36 percent of the schists of the Kittery formation and are an integral part of the rock matrix. In a few specimens, concentrations of sericite indi- cate originally argillaceous beds. Some sericite also occurs in veinlets and shears and, very commonly, as an alteration product of plagioclase feldspar.

Plagioclase feldspar, generally albite to andesine (A117..30 ) , is present up to 11 percent in some specimens. Detrital albitic plagioclase occurs in rocks of the lowest metamorphic grade; metamorphic andesine is an essential part of the actinolite- bearing schists in many places. Albite twinning is comnon in all thin sections. Alteration to sericite, epidote-zoisite, and carbonate is present in most thin sections. Near the fault contact with the Rye formation, grains of plagioclase feldspar are marginally granulated and exhibit bent and fractured twin planes.

Accessory chlorite, penninite and prochlorite, is present as alteration products of biotite and nowhere exceeds 12 percent of thg^tfchists. It is most abundant near or in areas of rock dis­ location. Porphyroblastic muscovite was observed in a few speci­ mens, equal in size to the biotite porphyroblasts, with which it is intergrown.

Epidote-zoisite occurs as disseminated grains and as an alteration of plagioclase feldspar. Some grains are closely associated with biotite and chlorite, possibly as alteration 57 produces of those minerals* Irregular masses of calcite are present in most specimens, some secondary after plagioclase, some perhaps the result of metamorphic reaction of dolomite vith quartz in the formation of actinolite, and some perhaps recrystallized from calcite in the original sedimentary rock.

Garnet, presumably almandine, was identified in but two specimens of schist from the Kittery formation. One garnet- bearing outcrop is approximately one mile southwest of Hampton, near the intersection of Lafayette Road and the Boston and Maine

Railroad, the other is about 0.5 mile southeast of Hampton Falls

Station, Hampton Falls. Under the microscope the garnet is anhedral, fractured, and partly altered to biotite.

Green actinolite, pleochroic in pale green, poikiloblastically includes irregular grains of quartz. Most of the actinolite-bearing schist occurs as a lithologic type transitional from biotite-rich schists to lime-silicate rocks. Accordingly, the orientation of the euhedral to subhedral actinolite blades ranges from a rigorous alignment in the foliation of the more schistose rock types, and in rocks adjacent to the fault contact with the Rye formation, to a random orientation in those rocks composed of abundant equi- dimensional minerals.

Apatite needles and prisms are ubiquitous and are contained, for the most part, in quartz and plagioclase. Euhedral to sub­ hedral grains of zircon are present in quartz and, with pleochroic 58

haloes, in biotite and chlorite. Subhedral grains of sphene

commonly contain cores of magnetite or rutile. Euhedral tourmaline, variety schorl, with olive or blue pleochroism, was observed in most thin sections from rocks of the biotite and garnet zones.

Pyrite cubes and anhedral grains, to 1.6 mm, were found in most

exposures of the Kittery formation. Limonite and hematite pseudo- morphs after pyrite were noted in many thin sections.

Quartzites

Quartzites, which constitute a relatively small percentage of

the Kittery formation, are nevertheless distinctive in the field.

In the chlorite zone, quartzites are light gray-green to dark gray

and weather gray-brown. They are massive, fine to very fine grained,

and commonly exhibit conchoidal fracture. In the biotite zone

quartzites are medium to dark gray with a purplish cast, and

granular. Near the fault contact with the Rye formation, quartzite

beds are sheared and finely granulated. Beds of quartzite range

from a fraction of an inch to 5 feet in thickness and are

intercalated with other lithologic types of the formation.

Veins of'calcite and milky quartz, and calcite-coated fracture

surfaces, are common throughout the Kittery formation. 59

The only minerals identifiable in hand specimen are red-brown biotite, as much as % mm in size, light-green grains of feldspar, and vitreous grains of quartz.

Varieties of quartzites identified from the Kittery formation are sericitlc quartzite, chlorite-serlcite quartzite, chloritic quartzite, sericite-plagioclase quartzite, biotite-plagioclase quartzite, and calcareous quartzite.

In thin section, quartz comprises as much as 79 percent of the quartzites and occurs as angular or subangular grains, some of which are detrital in origin and some recrystallized and metamorphic In origin. In those specimens in which recrystallization apparently has not obliterated original sedimentary textures, sorting is poor and quartz fragments are angular to subangular. In the more extensively metamorphosed rocks, quartz grains are subangular or sutured and interlocking, llndulatory extinction is common in nearly all specimens.

Fine flakes of sericite, well aligned in the matrix or concen­ trated in layers reflecting original composition, make up as much as 18 percent of the quartzite. Chlorite flakes and shreds, in part secondary after biotite, constitute no more than 10 percent of the quartzite beds. As determined microscopically, varieties of chlorite present are penninite and prochlorite. Plagioclase feldspar in quartzites, partly detrital and partly metamorphic, 60 ranges from albite to andesine (An^^). The more calcic plagio- clase Is confined to those specimens containing actinolite. All grains of plagioclase exhibit albite twinning. As much as 15 percent plagioclase was observed in quartzite.

Biotite is present mostly as fine interstitial wisps, although some specimens show porphyroblasts as much as .85 nna across poikilo- blastically enclosing irregular grains of quartz. Pleochroism is in light to medium brown. Calcite, composing up to 25 percent of some quartzite beds, is irregular interstitial material in the chlorite zone. Actinolite, to 0.37 mm in length, was observed in some thin sections as euhedral laths and fibrous aggregates poikiloblastically including anhedral quartz grains.

Euhedral to anhedral epidote-zoisite grains are present in all quartzite specimens, some as alteration products of plagioclase.

Minor accessory minerals are subhedral to anhedral sphene, euhedral apatite and tourmaline, haloed anhedral grains of zircon in biotite and chlorite, and anhedral pyrite, hematite, and limonite.

Lime-silicate rocks

Lenses and thin beds of lime-silicate rocks up to 2 feet in thickness are interbedded with, and are transitional to, other lithologic types of the Kittery formation in the biotite and garnet zones. They are most commonly massive, medium grained, granular, and light gray to light gray-green in color, weathering light gray- brown. Megascopic minerals are quartz, amphibole, and pyrite. 61

In chin section, essential minerals are quartz, actinolite, plagioclase feldspar, and in a few specimens, epidote-zoisite.

Quartz, which ranges in size from 0.018 mm to 0.165 mm, is angular to subangular and, in some specimens, rutllated. Some recrystal­ lized and sutured quartz grains occur in narrow elongate spears parallel to the foliation of the rock. Quartz grains range from

29 to 58 percent of the lime-silicate rocks.

Plagioclase feldspar, generally andesine (An3 i_4£), occurs as subhedral grains with albite twinning. Most specimens are moderately to greatly sericitized. Actinolite, pleochroic in light to medium green, is present as poiklloblastic porphyroblasts as much as 3/4 mm in length, which include grains of quartz and sphene. As much as

21 percent of the lime-silicate rocks is actinolite. Epidote- zoisite grains, disseminated throughout the rock and commonly associated with biotite and chlorite, average 8 percent of the lime-

silicate rocks. In one thin section, however, epidote-zoisite com­ prises as much as 46 percent.

Pale red-brown flakes of biotite, pleochroic in light yellow

to brown, occur as fine disseminations in the matrix and as porphyroblasts which include quartz grains. Biotite is also an

alteration product of actinolite. Pale green chlorite, pleochroic

in light green to olive, is secondary after biotite and actinolite

and commonly includes grains of quartz. Some chlorite is present in

fine crosscutting veinlets. 62

Anhedral calcite grains are closely associated with actinolite, epidote-zoisite, and sphene. Calcite veinlets are also present in many specimens. Other accessory minerals are euhedral to anhedral apatite, subhedral grains of sphene, same with rutile cores, fine interstitial wisps of sericite, and anhedral grains of zircon, which are surrounded by pleochroic haloes in biotite and chlorite.

Eliot Formation (Silurian?)

General statement

The Eliot formation was originally named Eliot slate by Katz

(1917, p. 169) for exposures of metamorphosed argillaceous sedi­ mentary rocks in Eliot township, Maine, northwest of Portsmouth,

New Hampshire, and was designated Carboniferous in age. However, because of the diversity of rock types and the relative paucity of slates in this unit, Freedman (1950, p. 455) redesignated it the

Eliot formation.

Billings (1955) included the Eliot formation in the more comprehensive Merrimack group south of Brentwood and Exeter,

New Hampshire. The writer, however, on the basis of detailed field and laboratory study, believes that the Eliot formation can be identified and distinguished from the Kittery formation in the southern part of the area and has so mapped it. 63

The Eliot formation occurs in two distinct northeast-striking belts in the Dover-Exeter-Portsmouth region* One portion of the unit is on the west flank of the Exeter anticline and is in contact with the older Kittery formation and the Exeter pluton on the east, and with the younger Berwick formation on the west. The larger, second belt of Eliot formation occupies the central part of the Great Bay syncline, which is between the Exeter and Rye anticlines* It is bordered on the east and west by the Kittery formation and is intruded by the Newburyport quartz diorite, the

Exeter diorite, and by several small bosses of diorite which are probably related to the Exeter pluton.

Contacts of the Eliot formation with the Kittery and Berwick formations are conformable and gradational* The Eliot formation is distinguished from the Kittery formation by a dominance of argillaceous rock types, as contrasted with the more quartz-bearing types of the Kittery formation. The contact of the two formations is somewhat arbitrary, because of interbedding of the units.

The contact of the Eliot formation with the Berwick formation

is based on the abundance of lime-silicate rocks in the Berwick

formation. Meyers (1940, p. 33) considered the two units to be in

fault contact because of an apparent abrupt change in metamorphic grade. The writer, on the other hand, observed a gradual increase

in the degree of metamorphism in the rocks from southeast to 64 northwest In the contact area of the Eliot and Berwick formations.

The relationship of these two formations is discussed in more

detail in the description of the Berwick formation.

The Eliot formation was tentatively assigned to the Silurian(?)

by Freedman (1950, p. 453), who estimated its thickness to be

6,500 feet.

Rocks of the Eliot formation belong to the quartz-albite- muscovite-chlorite subfacies, the quartz-albite-epidote-biotite

subfacies, and perhaps in part to the quartz-albite-epidote-

almandine subfacies of the greenschist facies. The absence of the

indicator mineral garnet, however, does not permit accurate

definition of the highest metamorphic subfacies of the Eliot

formation.

Because of the many lithologic varieties included in the

Eliot formation, and for convenience of discussion, rocks of this

unit are described under major headings of slates, phyllites,

schists, quartzites, and lime-silicate rocks. These rocks were

probably once beds and lenses of shales, sandstones, and somewhat

impure limestones. Approximate modal analyses of some representa­

tive specimens are given in Table 4.

Slates

Dark gray to black slates of the Eliot formation are quanti­

tatively very minor in occurrence. Those observed in the field

exhibit beds from ^ inch to 1 inch in thickness. Cleavage is 65 commonly at a high angle to bedding. Cleavage surfaces are

generally a lustrous silvery gray, due to the presence of seri-

cite, and are spottily stained by limonite derived from the decompo­

sition of pyrite. Weathering of the slates is to a dark gray-brown

color and, in a few outcrops, to a yellow-stained soft, punky,

and pitted decomposed material. Slate of the Eliot formation is moderately well exposed on the banks of the Oyster River in Lee,

south of Demeritt Hill, north of the road to Durham.

Microscopically, quartz, sericite, and chlorite are the

essential minerals. Grain sizes range from 0.009 mm to 0.114 mm.

Angular detrital quartz and feldspar, which comprise as much as

60 percent of some slates, are generally well sorted. Chlorite,

composing as much as 25 percent of the slates, includes epidote-

zoisite grains and exhibits the ultrablue interference colors of

penninite. Sericite, as fine wisps, comprises as much as 45

percent.

Minor accessories include anhedral pyrite grains, in part

altered to limonite, needles of rutile, and fragments of tourmaline,

probably detrital in origin. Possible carbonaceous material,

dust-like in thin section, was observed in black pyritiferous

slates from East Kensington township from a road cut approxi­

mately one mile south-southeast of Tappan Corners. 66

Phyllites

Phyllites constitute the most abundant lithologic type in the Eliot formation. They are dark gray to dark green, lustrous, fine grained, crinkled and folded. Beds range from 1/32 inch to

1/8 inch thick. No minerals are Individually large enough for megascopic identification, although narrow streaks and pods of granular dolomite are common In some phyllites. A typical exposure of phyllite, showing a fold and the relation of cleavage to bedding and the fold axes is shown in Plate VI.

In thin section, essential minerals are generally quartz, sericite, and chlorite; in some specimens albite and dolomite are prominent quantitatively. Grain sizes range from 0.009 mm for matrix minerals to 1.13 mm for metacrysts of dolomite, as shown in

Plate VII.

Angular to subangular quartz grains comprise as much as

57 percent of the phyllites, occurring as part of the phyllite matrix and in recrystallized thin lenses parallel to relict bedding.

Well aligned sericite, disseminated throughout the rock and, in some specimens, concentrated in thin beds which probably reflect original argillaceous seams, makes up as much as 62 percent of the phyllites. Some phyllites contain chlorite, as shreds and flakes, amounting to nearly 50 percent. A photomicrograph showing the texture of a phyllite specimen with incipient cleavage is given in Plate VIII. 67 PLATE VI

Outcrop of folded Eliot formation. Minor fold and crinkles in phyllite showing axial plane cleavage. Exposure is 1.3 miles west of Hayes School, Madbury, New Hampshire. 68

PLATE VII

Photomicrograph of dolomite porphyroblast in Eliot formation.

Large light mass is dolomite (d). Matrix materials are quartz,

sericite, and chlorite. One mile northwest of tfoodbury School,

Portsmouth, New Hampshire. (Plane polarized light.) 69

PLATE VIII

Photomicrograph of Incipient cleavage in the Eliot formation.

Crinkled phyllite bedding composed of fine grains of quartz, sericite, and chlorite is cut by shadows of incipient cleavage. Northwest slope of Demeritt Hill, Lee, New Hampshire. (Plane polarized light.) Subhedral grains of albite (An,.^) constitute as much as 20 percent of some phyllites and may include particles of both detrital and metamorphic origin* Most albite is moderately seri- citized and some contains chlorite. Dolomite metacrysts, such as that shown in Plate VII, are locally abundant in some phyllites in the chlorite zone of metamorphism.

Minor accessory minerals include euhedral apatite, subhedral sphene, rutile needles, irregular calcite grains, pyrite anhedra which are partly altered to limonite, wisps of biotite, blebs of epidote-zoisite, and subhedral to anhedral zircon.

Schists

Schists of the Eliot formation are present in the biotite zone of metamorphism and range from light to dark gray or black with a distinct purplish cast. The lighter colored portions of the schists are generally more quartzose and granular; the darker

layers are more biotitic. Beds in the schists range from paper-thin laminae to beds \ inch thick. Elongate flat lenses of carbonate-bearing material, white to light gray-green in color, are commonly interbedded with the more micaceous and quartzose

rocks. Most beds are crinkled and folded. 71

Megascopically identifiable minerals include dark red-brown flakes of biotite up to % mm in width, vitreous quartz grains to

\ ran, and calcite blebs to 3/4 ran. Biotite occurs as fine grains aligned in the foliation planes and as larger randomly oriented flakes, which suggest late or post-deformational recrystalli­ zation. Veins of milky or smoky quartz are present in nearly all outcrops,

Microscopically, quartz comprises from 10 to 56 percent of the schists and occurs as angular particles in the matrix and as recrystallized grains in elongate pods and lenses. Porphyroblasts of biotite, in part oriented and in part random, are as much as

1.14 ran in diameter. Poikiloblastically included in the larger biotite grains are quartz and plagioclase feldspar. The content of biotite in the schists ranges from 26 to 55 percent.

Plagioclase feldspar, albite to oligoclase (An^Q_^), consti­ tutes from 8 to 22 percent of some schists. Although most plagioclase appears to be of metamorphic origin, some, especially

in the lower part of the biotite zone, may be detrital. Albite

twinning is present in all specimens.

Accessory minerals of Eliot formation schists are irregular patches of calcite, anhedral epidote-zoisite grains, sericite wisps in the foliation, chlorite as a minor alteration of biotite, 72 euhedral schorlite, anhedral zircon grains with attendant haloes in biotite and chlorite, fine needles of rutile, prisms of apatite in quartz and plagioclase, and anhedra of pyrite, partly altered to limonite.

Quartzites

In both the chlorite and biotite zones, beds of quartzite as much as 3 feet thick are common. In the lower grade of meta­ morphism, most quartzite beds are light gray to light gray-green, fine-grained, massive, and dense, with only chlorite or sericite streaks to 1/16 inch thickness to indicate bedding. Weathering of the chlorite- and sericite-bearing quartzites is to light gray or brown. Limonite stains due to the decomposition of pyrite are common.

In the biotite zone, quartzites are light to dark brown with a purplish cast due to the presence of biotite. Weathering of these quartzites is to dark brown. Color banding, because of concen­ trations of either biotite or quartz, is conspicuous in a few exposures. Biotite porphyroblasts as much as 0.5 nxn in diameter were observed. Milky quartz veln3 and calcite-coated fracture surfaces are common.

Folds and crinkles were observed in quartzite beds in both the chlorite and biotite zones. 73

In thin section, essential minerals of the quartzites are quartz, calcite, biotite, plagioclase feldspar, and sericite.

Angular to subangular grains of quartz, ranging in size from

0.037 to 0.092 mm, comprise from 48 to 69 percent of the quartzites.

Some grains show undulatory extinction. Irregular and patchy calcite grains constitute as much as 20 percent of some quartzites.

Flakes of biotite, pleochroic from light brown to red-brown, occur as aligned and, in some specimens, randomly oriented plates making up as much as 17 percent of the rock.

Plagioclase feldspar, albite to oligoclase (An^j^), consti­ tutes up to 20 percent of the quartzites. Nearly all grains show albite twinning and are moderately sericitized. Although most of

the subangular grains are probably of metamorphic origin, some may be detrital, particularly those in the chlorite zone.

Well aligned wisps of sericite ccxnprise as much as 16 percent

of the quartzites. Most sericite occurs interstitial to quartz,

plagioclase, and calcite, but some is concentrated in thin seams

which probably reflect original sedimentary bedding.

Minor accessory minerals include chlorite, some derived

from the alteration of biotite, euhedral apatite in quartz and

plagioclase, anhedral grains of epidote-zoisite, aligned muscovite

flakes, sphene, rutile, anhedral pyrite, limonite, zircon grains in

quartz, plagioclase, biotite, and chlorite, and angular fragments

of tourmaline, which may be detrital in origin. 74

Lime-silicate rocks

Lease abundant in the Eliot formation are lime-silicate rocks, which occur in the biotite zone of metamorphism. Most are in thin beds or lenses gradational into other lithologic types of the unit and are fine to medium grained, massive, and granular in texture. The lime-silicate rocks are light gray-green and weather to light gray-brown. Only dark-green actinolite and white quartz grains are megascopically identifiable.

In thin section, angular to subangular quartz grains comprise as much as 52 percent. Green laths of actinolite, as much as

4 mm in length, are rigorously aligned at or near contacts with more schistose lithologic types and are randomly oriented within the beds or lenses of lime-silicate rocks. As much as 17 percent actinolite was observed.

Subangular grains of plagioclase feldspar, andesine in compo­ sition ( ^ 30 .32 ^ ’ constitute as much as 23 percent of the lime- silicate rock. Most are moderately sericitized. Epidote-zoisite grains are distributed throughout the rock, some as alteration products of plagioclase and actinolite.

Minor accessories are chlorite, which is an alteration product of actinolite, shreds of interstitial sericite, patches of calcite, euhedral apatite in quartz and plagioclase, anhedral grains of sphene, some with rutile cores, subhedral to anhedral zircon sur­ rounded by pleochroic haloes in actinolite and chlorite, and streaks of finely granular pyrite. 75

Berwick Formation (Silurian?)

General statement

The Berwick formation crops out west and northwest of the

Exeter pluton in the northwest part of the area mapped. The unit was originally named the Berwick gneiss by Katz (1917, p. 166-167)

for exposures in Berwick, Maine and Somersworth, New Hampshire.

Freedman (1950, p. 456) redesignated the unit the Berwick formation,

because of the varied lithologic content and the absence of true

gneissic rock types. Considered to be pre-Carboniferous, perhaps

Algonkian(?), in age by Katz (1917, p. 166-167, Plate 61), the

Berwick formation was subsequently assigned to the Silurian(?)

by Freedman (1950, p. 488) and Billings (1956, p. 103) on the basis

of a tentative correlation with fossiliferous rocks to the north­

east in Maine. The thickness of the Berwick formation was esti­ mated by Billings (1956, p. 42) to be 10,000 feet.

The Berwick formation is transitional with the older Eliot

formation on the east, and in the area where both units are in the

biotite zone they are very similar lithologically. In general,

however, there are more beds and lenses of lime-silicate rock in

the Berwick formation and a deficiency of quartzite beds. To the

west and southwest, however, Freedman (1950, p. 458) estimates that

quartzites comprise approximately 20 percent of the Berwick for­

mation in the Mount Pawtuckaway quadrangle. 76

Although the contact of the Berwick formation with the

Devonian Littleton formation is not exposedt the general structural conformity of the two units suggests at most a disconformity. The

Berwick formation is intruded in the northwest by quartz monzonite

and related pegmatite bodies.

The regionally metamorphosed rocks of the Berwick formation belong to the quartz-albite-epidote-biotite subfacies and the

quartz-albite-epidote-almandine subfacies of the greenschist

facies, and to the staurolite-almandine subfacies of the almandine-

amphibole facies, with the grade of metamorphism progressively

higher from southeast to northwest. In addition to the more

generally used indicator mineral garnet, which is very rare in the

Berwick formation, the presence of dlopside in the lime-silicate

beds and oligoclase and albite in the more pelitic rocks was

utilized to establish facies relationships.

Rocks of the Berwick formation in the Dover-Exeter-Portsmouth

region were probably once pelitic, semi-pelitic, and calcareous

sediments.

For facility of treatment, rocks of the Berwick formation

are discussed under the major categories of schists and lime-

silicate rocks. Approximate modal analyses of some representative

rock types are given in Table 5. 77

Schiats

The writer estimates that schists constitute at least 65 percent and perhaps as much as 75 percent of the Berwick formation.

Insufficient exposures preclude a more accurate evaluation. Host of the schists can be assigned to one of the three groups, plagioclase-quartz-biotite schists, biotite-sericite schists, or quartz-sericite-calcite schists.

Schists of the Berwick formation range from light gray in the quartz-sericite-calcite schists to dark gray or black in the more highly biotitic schists. Beds range from paper thin to

5 feet thick. Foliation of the schists is due to the planar orientation of biotite, sericite, and muscovite. Minerals megascopically identifiable in the schists are quartz grains,

flakes of biotite to 2 mm, sericite wisps, muscovite flakes to

1.5 mm, and anhedral pyrite to 1 mm. Milky quartz veins, which parallel and crosscut bedding and foliation, are commonly bordered

by selvages of biotite coarser than that present in the host rock.

In thin section, schists exhibit thin beds and laminae wl.ich

are minutely crinkled. Some layers are granular and composed

chiefly of grains of quartz and plagioclase, with minor inter­

stitial aligned sericite and biotite. Other beds are concen­

trations of parallel flakes of biotite or sericite. 78

The most common essential minerals in the schists of the

Berwick, formation are quartz, sericite, and biotite, although some varieties contain essential plagioclase, microcline, chlorite, or calcite. Quartz grains are generally angular to subangular and make up a large part of some schist matrices* Quartz was observed to range from trace amounts to 67 percent of some schists. Grain sizes range from .012 mm to .03 mm.

Sericite, as much as 40 percent, is well aligned parallel to planes of foliation, for the most part, and occurs either in discrete bands or S3 wisps disseminated throughout the rock.

Some sericite also occurs in narrow shears, oriented parallel to their walls. Biotite, pleochroic in light yellow to red-brown, amounts to as much as 60 percent of some schists; it is present

in all schistose rock types in the Kittery formation. Much of the biotite, especially the smaller flakes, shows a planar orien­ tation and is concentrated in thin layers or widely distributed

interstitially to other minerals. Poikiloblastic porphyroblasts of biotite, as shown in Plate VI, however, show no preferred

orientation and include quartz grains and shreds of sericite and previously formed biotite. These larger biotite flakes are

irregular in form and retain the bedding structure of the rock,

as shown in Plate IX. The maximum observed size of biotite porphyroblasts is 2 mm. 79

PLATE IX

.3MM-

PhoComicrograph of Berwick, formation showing biotite porphyro­

blasts. Large dark gray and irregular patches are biotite. Lighter matrix material is quartz, sericite, and pyrite. Relict bedding

is retained through biotite flakes. Cocheco River, 2.5 miles north­

west of Dover, New Hampshire. (Plane polarized light.) 80

Chlorite, pleochroic la light to dark green, is present as an alteration of biotite. In one thin section chlorite comprises

20 percent of the rock. Plagioclase feldspar, oligoclase

(Ani4_i7), occurs as subangular grains in the matrix. It is generally moderately sericitized and, in all specimens, shows albite twinning. The plagioclase content of the schists ranges

from 0 to 25 percent. In some specimens, angular to subangular grains of microcline are present in the matrix-as much as

15 percent. Irregular patches of calcite, comprising as much as

20 percent of the rock, were observed in a few thin sections

from rocks near the chlorite zone and the contact with the Eliot

formation on the north slope of Demerrit Hill, Lee.

Accessory minerals in the Berwick formation schists include

euhedral black tourmaline that is pleochroic in olive green.

Some specimens are zoned. Host prisms of tourmaline are randomly

situated. Rounded grains of epidote-zoisite, disseminated through

the schists, range from .05 mm to .03 mm and constitute a maximum

of 3 percent of the rocks. Other minor accessories include euhedral

apatite, subhedral to anhedral grains of pyrite partly altered to

limonite, muscovite flakes, rutile needles, and subhedral to

anhedral zircon surrounded by pleochroic haloes in biotite and

chlorite. 81

Lime-silicate rocks

Lenses and beds of lime-silicate rock, 1/16 inch to 3 feet in thickness, and transitional into other lithologic types, are common throughout the Berwick formation. They are white to light gray-green on fresh surfaces and weather to light chalky gray.

Although the rock is texturally moderately even and fine grained, random porphyroblasts of dark-green actinolite up to 4 an in length are present in many specimens. Stout forms of green diopside and pink garnet to 2 mm in size are present in a few specimens from outcrops adjacent to the quartz monzonite in

Barrington township. Grains of pyrite as much as 1 mm in width were observed in most lime-silicate rocks.

Microscopically the lime-silicate rocks are fine grained and of granoblastic texture, and contain randomly oriented porphyro­ blasts of actinolite, diopside, and garnet, probably grossularite.

Essential minerals of the lime-silicate rocks are quartz, plagio­ clase feldspar, actinolite, biotite, diopside, garnet, and calcite.

Angular to subangular quartz grains range from 0.018 mm to 1.006 mm in size and comprise from 29 to 50 percent of the rocks. Subhedral plagioclase, oligoclase-andeslne (A^j../^), makes up from 19 to

35 percent of the matrix of lime-silicate rock. Euhedral to subhedral poikiioblastic porphyroblasts of dark-green actinolite, shown in Plate X > are pleochroic in pale green. Included in actinolite are grains of quartz, sphene, zircon, magnetite, and 82 small flakes of biotite. Many blades of actinolite are zoned.

Patchy calcite appears to be in part secondary after actinolite.

Some porphyroblasts of actinolite are intergrown with large flakes of biotite and exhibit pleochroic haloes about zircon grains.

Actinolite ranges from 7 to 25 percent of the lime-silicate rocks.

Porphyroblasts of red-brown biotite, to 1.5 mm across, are common in some specimens. Included in the random flakes are sphene and zircon. Biotite was not observed to exceed 20 percent.

Locally, in lime-silicate rocks near the contact of the

Berwick formation with the quartz monzonite, diopside and garnet also are essential minerals. Blocky diopside prisms constitute from 15 to 20 percent of some specimens. Unzoned pink isotropic subhedral garnet, as much as 1.5 mm in size, probably grossularite, poikiloblastically includes quartz and magnetite grains. It com­ prises as much as 12 percent of the rock. In one thin section calcite, as interstitial grains and as veinlets, cemprises 20 percent of that specimen. In most samples calcite does not exceed

2 percent, occurring as interstitial patches and as an alteration of actinolite and plagioclase feldspar.

Accessory minerals include anhedral grains of epidote-zoisite, in part secondary after plagioclase and actinolite, sericite, euhedral and poikiloblastic tourmaline to 0.5 mm, subhedral zircon, chlorite, sphene, irregular grains and masses of pyrite partly altered to limonite, anhedral magnetite, and euhedral apatite. 83

A photomicrograph of typical lime-silicate rock is shown in

Plate X.

Littleton Pormation (Devonian)

The narrow northeast-striking wedge-shaped area of Littleton

formation mapped in the northwest part of the Dover quadrangle,

on the eastern border of the quartz monzonite, was originally

mapped as the Gonic formation by Katz (1917, p. 172-173) because

of the lithologic similarity with exposures to the north in

Gonic, New Hampshire. Although this segment of the Littleton

formation was not shown by Billings (1955), results of an extensive

reconnaissance survey by the writer into the Mt. Pawtuckaway

quadrangle to the west (Freedman, 1950) and the Berwick quad­

rangle to the north indicate that the rocks mapped by the writer

are part of the Littleton formation and not the Berwick formation.

Rocks of the Berwick formation are, with the exception of lime-

silicate beds, dark brown or gray, lacking in garnet, and generally

massive; rocks of the Littleton formation in the mapped area are

silvery gray, very schistose, and contain garnet and staurolite.

Originally the rocks were probably argillaceous.

The Littleton formation is in contact on the southeast with

the Berwick formation. There are no exposures of the contact

and there is no indication of a transition of rock types. 84

PLATE X

*3 « m -

Photomicrograph of Berwick formation showing actinolite porphyroblasts. Laths of random poikiloblastic actinolite in a matrix of quartz, plagioclase, calcite, and sericite. Cocheco

River, 2.5 miles northwest of Dover, New Hampshire. (Plane polarized light.) 85

Structural data, however, suggest a conformable relationship.

There Is also no metamorphic discontinuity between the two units.

Katz (1917, p. 172-173) considered the Littleton-Berwick contact a fault or unconformity. The writer found no evidence to substantiate this hypothesis.

On the northwest, the Littleton formation has been intruded by quartz monzonite. Although no contacts of the two were observed, the presence of pegmatites in the Littleton formation in the assumed contact area, in addition to the high metamorphic grade of the formation, suggests that the contact is an intrusive one.

Only two outcrops of the Littleton formation were found, one consisting solely of Littleton formation, the other primarily of pegmatite with but a thin selvage of metamorphic rock.

Megascopically, the Littleton formation, in the area mapped, consists of contorted silvery gray muscovite-biotite-staurolite- garnet schist. Beds range from 1/32 inch to 2 inches thick.

Compositional variations are expressed by concentrations of biotite and muscovite. In hand specimen, staurolite ranges from

4 ran to 1 cm, and garnet, presumably almandine, 2 mm to 4 mm.

Prisms of staurolite are random and appear to have been formed after cessation of regional movement. Rocks of the Littleton formation belong to the staurolite-almandlne subfacies of the almandine- amphibolite facies of regional metamorphism. 86

In thin section, quartz constitutes about 35 percent of the rock. It occurs as angular to subangular grains to 0.095 mm in the matrix and as thin pods parallel to the foliation.

Biotite porphyroblasts, as much as 2 ran in width and commonly randomly oriented, are pleochroic in yellow to dark red-brown.

They poikiloblastically include angular quartz grains and smaller earlier formed shreds of biotite. Biotite makes up as much as

18 percent of the schist.

Large porphyroblasts of muscovite, as much as 0.80 mm in size, comprise a maximum of 22 percent of the schist. They are generally intergrown with biotite and most are parallel to the foliation of the schist. Random prismatic porphyroblasts of staurolite, with sieve-like structure, constitute as much as

25 percent of the schist and are as much as 3.43 mm in length.

Angular quartz grains are poikiloblastically included in staurolite.

Porphyroblasts of dodecahedral garnet, to 4 mm in size, are conspicuous in the Littleton formation. Quartz and magnetite grains are poikiloblastically included in garnet, which comprises apprcximately 12 percent of the schist.

Accessory minerals of the Littleton formation are fine shreds of interstitial sericite, chlorite derived from biotite and staurolite, anhedral pyrite, magnetite, and zircon, and euhedral tourmaline. INTRUSIVE IGNEOUS ROCKS

General Statement

Bodies of intrusive igneous rocks in the Dover-Exeter-

Portsmouth region range in size from narrow dikes and sills to

large plutonic masses and in composition from granite and pegma­ tite to gabbro and camptonite. Billings (1956, p. 65-69) has assigned the quartz monzonite of Rochester and Barrington, the

Exeter diorite and related smaller bodies of diorite, and the granite intrusive into the Rye formation, which the writer has designated the Breakfast Hill granite, to the Upper Devonian(?)

Hillsboro plutonic series. The writer also includes in the Hills­ boro plutonic series the Newburyport quartz diorite and the porphyritic quartz monzonite of Seabrook, New Hampshire.

Billings, on the other hand, considered the Newburyport quartz

diorite to be Precambrian or Early Paleozoic in age (1956,

p. 45-46) and correlated the porphyritic quartz monzonite with

the Ayer granodiorite of eastern Massachusetts. Reasons for the

differences in assignment are discussed with those two units.

Camptonite dikes and sills, which are intrusive into all

other units, both metamorphic and igneous, are assigned by Billings

(1956, p. 86) to the Mississippian(?) White Mountain plutonic-

volcanic series. Although bodies of camptonite are very numerous,

none are large enough to be shown at the scale of the map.

87 88

The lone granophyre dike observed during the investigation also is referred to the White Mountain series by the writer.

Only the Exeter diorite, in the area mapped, has been dated by the lead-alpha method, Lyons et al (1957, p. 535) cite.a

307i 10 m.y. age for the diorite and classify it as part of the

New Hampshire magma series. According to Kulp's geologic time

scale (1961, p. 1111), 307 m.y. is Pennsylvanian in age. However, because of uncertainties in the lead-alpha system of age determi­

nation, the lack of several substantiating dates from the Exeter

diorite, and the absence of corroborating dates by other methods,

particularly potassium-argon and 3 trontiura-rubidium analyses,

Henry Faul (personal communication, 1958) advised extreme caution

in the use of an absolute date for the Exeter diorite. Conse­

quently, the plutonic series age assignments used in this paper

are those of Billings.

Hillsboro Plutonic Series

General statement

The designation Hillsboro plutonic series was first used

by Billings (1956, p. 65-66) to include those intrusive igneous

rocks of southeastern New Hampshire which possess characteristics

similar to those of the Upper Devonian(?) New Hampshire plutonic

series. Like the rocks of the New Hampshire plutonic series, those 89 of the Hillsboro series are considered to be in part synchronous with the Acadian orogeny in New England.

Inasmuch as the various lithologic units of the Hillsboro plutonic series were not found in contact with one another in the area mapped, accurate determination of relative ages was not possible. Lacking more specific evidence, the writer has arranged the units of the Hillsboro plutonic series in an order of decreas­ ing foliation and granulation, on the assumption that these intrusive igneous rocks range from syntectonic to late- or post- tectonic.

In the order mentioned above are the Breakfast Hill granite and pegmatite, the Newburyport quartz diorite, porphyritic quartz monzonite, the Exeter diorite, and quartz monzonite.

Breakfast Hill granite and pegmatite

Granite and pegmatite confined to the Rye formation and previously referred to as "mylonitized crystallines" by Meyers

(1940, p. 32) and as "granite" by Billings (1956, p. 68), are here named the Breakfast Hill granite and pegmatite. At the type locality, Breakfast Hill, which is situated on the township boundary between Rye and Greenland, the granite and pegmatite are white to light gray on fresh surfaces and chalky white or tan on weathered surfaces. The rocks range from medium to coarse grained to pegmatitic and are massive to gneissic. 90

Although only Breakfast Hill consists of outcrop large enough to be shown at the scale of the map, representatives of this unit occur elsewhere throughout the Rye formation, ranging from pegmatitic seams less than an Inch in thickness to bodies of granite and pegmatite 30 feet thick. Billings (1955), as a result of reconnaissance study, indicated on his geologic map of

Hew Hampshire a large belt of granite in the Rye formation. No such single large mass of granite Is present, but virtually no outcrops of the Rye formation are lacking in granite or pegmatite, and many exposures owe their existence to the bulwarking nature of the Breakfast Hill granite and pegmatite.

Megascopically identifiable in outcrops of the granite and pegmatite on Breakfast Hill are quartz, microcline, plagioclase, and muscovite. Pink garnet and black tourmaline are present in

some exposures of pegmatite. Microcline ranges from euhedral

crystals as much as six inches in length to augen as much as

1% inches in length and anhedral grains in granite as much as

1/16 inch in diameter. The plagioclase, which is generally white

as contrasted to the cream or light tan of the microcline, is

subhedral to anhedral and, in most exposures, is subordinate in

amount to microcline. In the more highly deformed parts of the

rock, plagioclase is also augen-shaped. Muscovite, where present,

is concentrated on foliation surfaces and is as much as 3/4 inch

in diameter in the pegmatite. Pink garnet euhedra are not uncommon 91 in the pegmatite and are as much as 1/8 Inch In diameter* Some garnet, particularly that In foliated pegmatite, shows fracturing and some dispersal of fragments. Black tourmaline crystals, same one Inch in length and % inch in diameter, are also a common constituent of the pegmatite. Where foliation is strongly developed

in the pegmatite, tourmaline is greatly shattered and dispersed parallel to the foliation, as shown in Plate XI.

In other exposures of the Breakfast Hill granite and pegmatite a minor amount of biotite was observed, which is interpreted here as a contaminant through reaction of the granitic material with

the metamorphic host rock. Where inclusions of blotite schist or

amphibolite are present, biotite is locally abundant in the granite

and pegmatite on foliation surfaces.

Most bodies of granite and pegmatite are concordant, ranging

from thin veins or seams of pegmatite intimately penetrating along

foliation planes of the Rye formation to lenses as much as 30 feet

across dilating the bedding and foliation. Locally crosscutting

relationships are apparent, as shown in Plate XII. In several of

the larger lenses there is a gradation from marginal granite, very

strongly foliated parallel to the contact with the enclosing metamorphic rock, to a core of massive and undeformed pegmatite.

Where both the granite and pegmatite are present in an outcrop,

the contact of the two is in all cases gradational. PLATE XI

Outcrop of Breakfast Hill pegmatite lens in lower member of the Rye formation. Granulated tourmaline fragments in

"pinch-and-swell" lens of pegmatite. Rye North Beach, Rye,

New Hampshire. PLATE XII

Outcrop of folded Breakfast Hill pegmatite in the lower member of the Rye formation. Granulated pegmatite folded against deformed metamorphic rocks. Rye North Beach, Rye, New Hampshire. 94

In a few places, the marginal granulation and imposed secondary foliation of the granite and pegmatite lenses are sufficiently severe to produce a light gray, streaked, porcelain-like rock, which was identified through field and microscopic study as myIonite developed from granite or pegmatite. This supports the writer's hypothesis that the greatest relief of stress was concen­ trated at the contacts of greatly differing lithologic rock types.

In all cases, the enclosing metamorphic rocks are but slightly more deformed cataclastically at or near contacts with the granite or pegmatite lenses than elsewhere.

A very few dike-like bodies of pegmatite were found, and these, crosscutting the foliation and bedding of the Rye formation, are highly deformed into "S" shapes. That deformation of the region continued after the emplacement of the pegmatite is shown by the splaying out of the metamorphic rocks at the contact with

the points of reversal in the "S" shapes of the pegmatites and

by mylonitization of the igneous rocks near their contacts with

the enclosing metamorphic rocks.

Many of the smaller pegmatite bodies possess a

"pinch-and-swell" structure. Although these bodies are roughly

concordant, crosscutting relations are common on a very minor

scale. 95

Many bodies of granite and pegmatite show lineations similar to those in the Rye formation. Foliation surfaces with corru­ gations to % inch in amplitude and two inches in wave length,

trains of muscovite, and, much less common, trains of fragmented tourmaline constitute the linear elements.

Billings (1954, p. 319-320) gives as criteria of syntectonic

intrusions the granulation of minerals, particularly along contacts, folded apophyses of such Intrusions, and the general

concordance of lenses or sheets of the Intrusive material. He also

cites primary foliation as characteristic of some syntectonic bodies.

Billings (1956, p. 68-69) places the Breakfast Hill granite

in the Hillsboro plutonic series, which he equates inferentially

with the New Hampshire plutonic series of Upper Devonian(?) age,

which is in part syntectonic.

Microscopically, the Breakfast Hill granite and pegmatite

are composed essentially of quartz, microcline and microcline- microperthite, and plagioclase. Quartz occurs as anhedral inter­

stitial grains in the more massive and undeformed bodies and as

crushed, partially recrystallized elongate, spear-like pods.

Much of the quartz shows strain shadows. Post-pegmatite quartz

veinlets crosscut most other minerals. Quartz ranges from

12 to 25 percent of the rock. Microcline and microcline~microperthite comprise as much as

65 percent of the granite and pegmatite. In most specimens the potassic feldspar is fractured or granulated. Microcline augen are most common near the margins of granite or pegmatite bodies

and exhibit trails of granulated microcline in the quartz matrix.

Microcline is subhedral to euhedral in the central part of the

igneous masses. Inasmuch as cataclasis is greatest at the

contacts of the igneous lenses with the metamorphic rocks, euhedral microcline is found primarily in the cores of thicker pods of

pegmatite and granite. Microcline. is myrmekitically intergrown

with plagioclase in many thin sections, and includes serlcitized

fragments of it.

According to Marmo (1956, p. 481, 1958, p. 363), microcline,

rather than orthoclase, occurs in syntectonic and late tectonic

granites because of appropriate temperatures and slow cooling,

which induce unmixing of the potassic and sodic portions of the

feldspar. By this hypothesis, the presence of microcline, rather

than orthoclase in the Breakfast Hill granite and pegmatite,

supports the proposed syntectonic origin of these rocks.

All plagioclase * ranging from albite to oligoclase,

is slightly sericitized and shows albite twinning in nearly all

specimens. Much of the plagioclase is bent and fractured. 97

Enclosed In plagioclase are shreds of biotite and muscovite,

Myrmekitic intergrowths between (1) plagioclase and microcline and (2) plagioclase and quartz are very common, Oligoclase is most abundant in pegmatite, comprising as much as 43 percent.

Albite is most abundant in granite.

Biotite, in general, is pleochroic in light yellow to red- brown, although some biotite, containing aciculae of rutile, is pleochroic in light olive. The latter variety may represent a retrogressive transition between the more normal biotite and chlorite. Most biotite occurs in granite and pegmatite near the contacts with biotite-rich schists and amphibolites and adjacent to inclusions of those rocks. Apparently reaction of the granitic intrusive material with amphibole has resulted in the production of biotite from hornblende. Movement during crystallization has somewhat dispersed flakes of biotite along and parallel to the foliation planes. Additional evidence that biotite is a contaminant is found in the presence of fibrolltic slllimanlte intergrown with biotite in several specimens.

Chlorite, which is secondary after biotite, is pleochroic in light green and shows the ultrablue interference color of penninite. Needles of rutile and rounded grains of magnetite are common Inclusions. 98

Muscovite, where present, occurs as large flakes bent around feldspar augen, as fine shreds interstitially, and as an alter­ ation of sillimanite. Much of the muscovite is intergrown with biotite and is broken and shredded parallel to the foliation.

Sericite, which comprises as much as 10 percent of the rock, occurs as an alteration of plagioclase and as wisps in the cleavage and fractures of plagioclase.

Pink garnet, probably almandlne, ranges from euhedral dodeca- hedra, to strained and slightly anisotropic fractured crystals, to dispersed fragments. Biotite and chlorite are alterations marginal to and in fractures in garnet. Some fractures in garnet are healed by albitic plagioclase.

Sillimanite, although rare in the granite and pegmatite, constitutes a contamination product, derived from adjacent aluminous metasediments. It is generally in flamboyant fibrous aggregates partly replaced by muscovite and partly intergrown with biotite.

Sillimanite needles were also observed in feldspar and quartz.

Tourmaline ranges from euhedral crystals to fragmented and dispersed particles in the folia. It is pleochroic from colorless to brown and is most abundant in the pegmatite. Only rarely were

fine needles of tourmaline seen in the granite.

Epidote-zoisite is present as an alteration of plagioclase, as thin veinlets crosscutting all other minerals, and as anhedral grains in biotite and chlorite. Some epidote-zoisite also occurs

in fractures of plagioclase and in trains along the cleavage of chlorite. 99

Of the minor accessories, zircon occurs as euhedral to anhedral grains in quartz, feldspar, muscovite, biotite, and chlorite* In

the last two, pleochroic haloes surround zircon. Magnetite grains

and irregular masses are associated with biotite and chlorite*

Apatite euhedra are present in quartz and feldspar. Calclte is

a very minor alteration product of plagioclase. Sphene, in

irregular masses, occurs widely disseminated throughout the

granite and pegmatite.

Representative approximate modal analyses of the Breakfast

Hill granite and pegmatite are given in Table 6 .

Hewburyport quartz diorite

The Newburyport quartz diorite, which was mapped in the

southeastern corner of New Hampshire in Hampton Falls and Seabrook,

was originally named by Emerson (1917, p. 177-178) for exposures

in the city of Newburyport, Massachusetts, four miles south of

Seabrook, with which the New Hampshire exposures are probably

continuous.

Emerson (1917, p. 164, 172-181) and Clapp (1921, p . 12), on the

basis of studies in eastern Massachusetts and, particularly,

Essex County, Massachusetts, considered the Newburyport quartz

diorite to be part of a Devonian(?) batholithic Igneous complex

which Included the Salem diorlte-gabbro, the Newburyport quartz

diorite, and the Dedham granodiorite as successive products of

differentiation from a single magmatic source. LaForge (1932, 100 p. 21-22) considered Che complex Co be pre-Devonian. Dowse

(1950, p. 95-99) reporced fossiliferous Lower Cambrian slaCes rescing unconformably on Dedham granodloriCe aC Hoppin Hill,

North ACCleboro, Massachusecta. By the presumed relaCionship of

Che Newburyporc quartz diorite Co the Dedham granodlorite and by

Che presumed correlation of Che Dedham granodiorite from north­ eastern Massachusetts to North Attleboro, Massachusetts, near the

Rhode Island state boundary, Billings (1956, p. 106) gave a

Precambrian age to the Newburyport quartz diorite. In an earlier publication, however, Billings (1952, p. 25) allowed the possi­ bility that the Newburyport quartz diorite might be a member of

the New Hampshire magma series, which he later designated the

Upper Devonian(?) Hillsboro plutonic series in southeastern New

Hampshire (Billings, 1956, p. 65-66).

The writer agrees with Billings' statement that the Newburyport

quartz diorite might belong in the Hillsboro plutonic series,

inasmuch as this igneous rock unit possesses characteristics more

appropriate to Billings' criteria for the Hillsboro series than for

the others (1956, table 12). In addition, inclusions of metamorphic

rock lithologically very similar to the Klttery formation were

observed in the Newburyport quartz diorite. Thus, if the Kittery

formation is Silurian(?), and if the inclusions are truly of the

Kittery formation, the Newburyport quartz diorite can be no older

than Silurian(?). 101

In the field, the Newburyport quartz diorite is medium to coarse grained, crudely foliated, and light to medium gray, weathering to dull light gray or white. Abundant angular to subangular inclusions of metasediments and inclusions or schlieren of black diorite are common. Those foreign fragments which are elongate in shape are generally poorly to well aligned with the foliation of the quartz diorite. Nowhere does the foliation of the quartz diorite continue through inclusions. Some inclusions have a maximum dimension of five feet.

Most inclusions of metamorphic rocks, which were tentatively identified as Kittery formation and Rye formation types, show well defined boundaries with the quartz diorite. Some of the minerals identified in the metasedlmentary inclusions are anda- lusite, sillimanite, quartz, feldspar, biotite, chlorite, and muscovite. It could not be determined what proportions of these minerals were present as products of the metamorphic effects of the quartz diorite. It should be noted here, however, that although the contact of the Newburyport quartz diorite with the

Kittery or Eliot formations was not seen in the field, outcrops of those formations that are nearest to known exposures of the quartz diorite show a maximum elevation in metamorphic grade to only the quartz-albite-epidote-biotite subfacies of the green- schist facies. 102

The dioritic inclusions or schlieren show both sharp and diffuse borders, and the presence of feldspar porphyroblasts in some fragments, as much as 3 mn in length, particularly near the contacts, suggests a permeation of the fragments by the quartz diorite when it was at least partially mobile.

It is the opinion of the writer that the foliated dioritic fragments are autoliths of an intrusive igneous facies preceding that of the quartz diorite that were plucked from their original positions at the intrusion walls and borne upward to their present positions by the surge of differentiated quartz diorite magma.

Although foliation in both the diorite and the quartz diorite is primary, the foliation in some specimens of the diorite is

slightly distorted. It also seems significant to the writer that

the two areas of outcrop that contain the greatest abundance of

diorite fragments are near the assumed contact of the Newburyport

quartz diorite with the Kittery formation. One of the areas is

New Zealand Hill, Seabrook, 0.75 mile west of the town of Seabrook,

and the other is at the end of a dirt road 1.2 S miles east of

Dearborn School, Seabrook.

Billings (1956, p. 46) reported an intrusion breccia at

Beckmans Point on the seacoast 3 miles east of Seabrook. The

rock types involved in the breccia are like those identified in

other outcrops where diorite fragments have been suspended in a 103 matrix of quartz diorite. The sole difference lies in the super­ abundance of the more mafic rock types and the relative paucity of the more silicic quartz diorite which, at Beckmans Point, occurs only as thin seams and veinlets.

In addition to the Newburyport quartz diorite and its inclusions of metasediments and diorite, many bodies of pegmatite were observed in the quartz diorite. All pegmatites are in sharp contact with the enclosing quartz diorite and show microcline crystals up to 3^ inches in length. . Plagioclase and quartz are other major constituents. Biotite, chlorite, and muscovite are quantitatively minor.

No contact of the Newburyport quartz diorite with the porphyritic quartz monzonite to the south was observed in the field.

Approximate modal analyses of the quartz diorite, diorite inclusions, and pegmatite are given in Table 6.

Quartz diorite, the principal lithologic type in the

Newburyport quartz diorite complex, is light to medium gray, medium

to coarse grained, foliated, and commonly limonite stained.Minerals

identifiable in hand specimen are quartz, plagioclase, amphibole, biotite, and chlorite. Foliation is defined by the parallel to

subparallel orientation of micas, amphibole, and feldspar prisms. 104

Microscopically the quartz diorite ranges from hypldiomorphlc granular to foliated* Quartz comprises as much as 30 percent of the rock* It is granular or sutured and interlocking* Undulatory extinction was observed in quartz in many thin sections and thin veinlets of granular quartz crosscut feldspar and sutured quartz grains.

Plagioclase, ranging from oligoclase to andesine (^25-46^* shows albite twinning which, in some specimens, is bent and broken*

Normal zoning was observed in a few grains. Most plagioclase is moderately to heavily sericitized and includes euhedral prisms of apatite and anhedral grains of magnetite and amphibole. Epidote- zoisite is also an alteration product of plagioclase. Plagioclase constitutes from 40 to 67 percent of the quartz diorite.

Hornblende, pleochroic in light yellow**green to medium blue- green, is commonly twinned and occurs, in part, as an alteration of pyroxene. Hornblende amounts to as much as 20 percent of a specimen. Subhedral grains of sphene and anhedral grains of epidote- zoisite occur as inclusions.

Biotite, pleochroic in pale yellow to red brown, is partly an alteration product of hornblende. Many specimens contain acicular

inclusions of rutile(?). Epidote-zoisite grains are present marginally and along cleavage traces. Biotite is, in many instances, mostly altered to chlorite. As much as 19 percent of the rock is

composed of biotite. 105

Chlorite, which shows colorless to pale yellow-green pleochroism, exhibits the ultrablue interference colors of penninite and is a common alteration product of hornblende and biotite. Inclusions are epidote, along cleavage planes, and needles of rutile. Chlorite comprises as much as 14 percent of

the quartz diorite.

Augite, pleochroic in light green, comprises as much as 6 percent of the rock. It generally occurs as unaltered relicts in hornblende.

No more than 6 percent microcline, showing grid structure, was

observed in any specimen.

Minor accessories of the quartz diorite include sericite, an

alteration of plagioclase; epidote-zoisite, which occurs both as an

alteration of plagioclase and in thin crosscutting veinlets; apatite

euhedra in quartz, plagioclase, biotite, and hornblende; magnetite

grains in plagioclase, biotite, chlorite, and hornblende; euhedral

to anhedral zircon in plagioclase, hornblende, biotite, and chlorite,

with attendant pleochroic haloes in the micas; euhedral to subhedral

sphene in biotite; and calcite in crosscutting veinlets.

Diorite inclusions in the Newburyport quartz diorite are dark

gray to black, medium grained, and moderately to well foliated.

Plagioclase as much as 3 ran long and amphibole as much as 5 mm long

are megascopically identifiable. Some inclusions, as those of the

breccia at Beckmans Point, are laced by thin veinlets of quartz 106 diorite. At the contacts of the diorite with quartz diorite, bio­ tite as much as 3 mn in diameter is common. Feldspar porphyroblasts, which were probably introduced by the quartz diorite, are present in the diorite margins.

Microscopically the diorite is a medium-grained foliated rock in which plagioclase and amphibole and, in some places biotite, are the chief mineral constituents. Plagioclase grains are almost without exception heavily sericitized and in many specimens albite twinning is obscured by the sericitic alteration. Normal zoning was observed in many specimens. Plagioclase comprises as much as

58 percent of the diorite. Hornblende, showing colorless to pale blue-green pleochroism, is commonly twinned and includes subhedral plagioclase. Hornblende ranges from 18 to 57 percent of the rock.

Biotite is pleochroic in light yellow to red brown and contains many fine needles of rutile. It is an alteration of hornblende in many thin sections and attains a maximum of 18 percent of the diorite.

Chlorite is an alteration of biotite and hornblende and is pleochroic in light yellow to light green, with ultrablue interference colors.

It makes up, at most, 15 percent of the rock.

Minor accessories of the diorite include sericite and epidote- zoisite, which are alterations of plagioclase. Epidote-zoisite is also an alteration of hornblende, and, in addition, occurs as grains along cleavage planes of biotite and hornblende. Calcite is present secondarily after plagioclase and hornblende. Magnetite grains 107 occur in hornblende, biotite, chlorite, and plagioclase# A minor amount of quartz occurs as interstitial grains and as fine veins cutting feldspar and hornblende# Euhedral zircon with pleochroic haloes was noted in biotite. Subhedral to anhedral grains of sphene are present in biotite and hornblende. Euhedral apatite is ubiquitous.

Many bodies of pegmatite were observed in the Newburyport quartz diorite, most of them parallel to the foliation in the host.

Microcline crystals as much as 3% inches in length were noted.

Contacts of the pegmatite with the enclosing quartz diorite are sharp, for the most part, although some pegmatite bodies exhibit a rapid transitional decrease in grain size to that of the quartz diorite. Quartz, microcline, and plagioclase were identified megascopica1ly•

Microscopically the pegmatite shows minor granulation marginal

to feldspar and sane recrystallization of quartz. Quartz consti­

tutes as much as 30 percent of the rock and occurs as grains inter­

stitial to feldspar and as veinlets filling fractures in feldspar.

Phenocrysts of microcline-microperthite, commonly gridded, show some

distortion of lamellae. Many are twinned according to the Carlsbad

law and many include fragments of plagioclase. Plagioclase,

albite-oligoclase ( ^ 5-15) , forms approximately 20 percent of the

pegmatite. It most commonly shows albite twinning and a minor

amount of marginal granulation. Serlcitization of plagioclase

ranges from negligible to moderate. 108

Of the minor accessories, sericite and epidote-zoisite are alterations of plagioclase. Zircon euhedra occur in plagioclase and microcline. Apatite prisms are present In quartz and feldspar.

Chlorite wisps, perhaps secondary after biotite, show colorless

to light-green pleochroism.

Porphyritic quartz monzonite

In extreme southeastern New Hampshire, near the juncture of

the Massachusetts state boundary and the seacoast, is a small

irregularly shaped body of igneous rock that consists principally

of porphyritic quartz monzonite, with lesser amounts of equi-

granular quartz monzonite, pegmatite, and aplite. Billings (1955,

1956, p. 68) considered this body of rock to be a part of the

Ayer granite of Emerson (1917, p. 223-228), because of its lithologic

similarity. The writer, however, who has mapped and studied

porphyritic Ayer granite to the southwest in Massachusetts,

disagrees with the correlation.

Geographically, the nearest body of Ayer granite is approxi­

mately 35 miles to the southwest. The porphyritic quartz monzo­

nite of southeastern New Hampshire is generally crudely foliated

and contains numerous bodies of pegmatite and aplite; the Ayer

granite contains few, if any, pegmatite bodies and only a few 109 aplite dikes. Aplites of the New Hampshire intrusive contain garnet and tourmaline; aplites of the Ayer granite do not.

Phenocrysts of the New Hampshire quartz monzonite are intact; most phenocrysts of the Ayer granite are broken or faulted.

There is some evidence, however, to support the hypothesis that the porphyritic quartz monzonite of Seabrook is a facies of

the Newburyport quartz diorite. In New Hampshire and, as ascertained by limited reconnaissance to the south in Salisbury,

Massachusetts, the porphyritic quartz monzonite is contained within

the body of Newburyport quartz diorite. The contact of the

quartz monzonite with the quartz diorite is nowhere exposed.

However, there is no apparent decrease of grain size in exposures

of either rock type near the presumed contact, and the quartz monzonite contains inclusions of rock types which, in outcrop,

appear to be identical with those found in the quartz diorite.

It is the writer's opinion that the porphyritic quartz monzonite

is a magmatic differentiate of the Newburyport quartz diorite and

is, in essence, part of the same intrusive episode. Thus the

quartz monzonite is also included in the Upper Devonian(?) Hillsboro

plutonic series by reason of its apparent relationship to the

Newburyport quartz diorite. 110

Foliation in the quartz monzonite is poorly to moderately well developed, and elongate inclusions of metasediments and

diorite are crudely aligned with the foliation. The foliation

observed in some inclusions, however, is not parallel with that

of the quartz monzonite.

Excellent exposures of the quartz monzonite with inclusions

of several lithologic types are located in roadcuts approximately

0.75 mile west of Majors Rock in Seabrook.

The porphyritic quartz monzonite is medium to coarse grained,

porphyritic, medium gray, and hypfdiomorphic granular to moderately

well foliated. Phenocrysts of cream to light-gray euhedral micro-

cline as much as three inches in length are not uncommon. The

foliation, which is interpreted as primary on the basis of both

field and laboratory study, is expressed by a parallel to sub­

parallel alignment of feldspar phenocrysts, and oriented amphi­

bole, biotite, and chlorite. It is accentuated in many places

by the presence of elongate inclusions oriented parallel with the

foliation of the host.

Microscopically the porphyritic quartz monzonite is composed

essentially of quartz, plagioclase, and microcline. Quartz occurs

as anhedral grains filling irregular interstitial spaces among

other minerals, as strained sutured and interlocking grains, Ill probably recrystallized, and in thin late-stage veinlets cross­ cutting plagioclase, microcline, and amphibole. Quartz ranges from 11 to 25 percent of the rock.

Oligoclase-andesine (^29-41^* ran6 in8 from 39 to 46 percent, most coomonly exhibits albite twinning ~ahd moderate sericiti- zation. Normal zoning was observed in some specimens. Myrmekitic intergrowth of plagioclase with quartz is present in some samples.

Microcline and microcline-microperthite, which range from

23 to 42 percent, show grid structure and commonly enclose sericitized plagioclase, hornblende, biotite, and chlorite.

Although most of the microcline occurs as phenocrysts, a very minor amount is present in the groundmass.

Both plagioclase and microcline show minor marginal granu­ lation. Some plagioclase grains exhibit bent and fractured twin lamellae.

Hornblende shows twinning, is pleochroic in light yellow to pale blue-green, and does not exceed 8 percent of the rock.

Anhedral grains of epidote-zoisite, magnetite, and zircon, and euhedral apatite are common inclusions. Alteration of hornblende to biotite, chlorite, epidote-zoisite, and calcite has been observed in thin section. In a very few specimens small fragments of colorless augite were noted in hornblende. 113 112 Nonporphyritic quartz monzonite, which is present very locally Biotite, pleochroic in light yellow-brown to dark red-brown, in the intrusive, differs from the porphyritic type only in that occurs as individual flakes and as an alteration of hornblende, the microcline and microcline-microperthite are not phenocrysts, Biotite, in turn, is partly altered to chlorite. In no thin Compositionally, mineral percentages are very similar in both rock sections does biotite exceed 11 percent. types, Chlorite, exhibiting light yellow to light green Enclosed in the porphyritic quartz monzonite are pieces of pleochroism, shows ultrablue interference colors of penninite, metasedimentary rocks, some of which megascopically greatly It generally contains acicular inclusions, probably rutile, and resemble parts of the Kittery formation, and diorite fragments, grains of epidote-zoisite along cleavage traces, Chlorite which can be autoliths similar to those in the Newburyport quartz averages 1 percent of specimens, but has a maximum of 15 percent diorite, in one thin section, Diorite inclusions are in part massive and in part foliated, Minor accessory minerals in the porphyritic quartz monzonite All are dark gray to black and medium to coarse grained, are many, Of these minerals, epidote-zoisite grains are alter­ Identifiable megascopically are light gray plagioclase feldspar ations of plagioclase and hornblende and are included in horn­ and black amphibole, blende and chlorite; sericite is present as an alteration of In thin section the diorite is composed chiefly of plagio­ plagioclase; colorless augite fragments are included in hornblende; clase and amphibole, Plagioclase, which comprises as much as anhedral grains of magnetite are present in epidote and horn­ 46 percent, is moderately sericitized and is commonly inter­ blende; euhedral to subhedral sphene and euhedral apatite are grown myrmekltlcally with accessory quartz, The composition is disseminated throughout the rock, Calcite occurs as an alter­ andesine (An^.^) in those specimens studied, Albite twinning ation of plagioclase and hornblende, as a mineral associated with is present in nearly all plagioclase, epidote-zoisite, and in thin veinlets crosscutting other minerals, Hornblende, pleochroic in light yellow to medium green, Zircon grains are present in hornblende, biotite, and chlorite, Incloses euhedral apatite and is partly altered to epidote- with surrounding haloes in the last two minerals, zoisite, Hornblende makes up as much as 38 percent of a specimen, 114

Chlorite, pleochroic in yellow to light green, is an alter­ ation o£ hornblende and perhaps biotite, although no traces of unaltered biotite are present. Interstitial anhedral grains of quartz are very minor in amount. Other minor accessory minerals are anhedral grains of epidote-zoisite, in part secondary after plagioclase and hornblende, euhedral apatite, and anhedral to sub­ hedral sphene.

Bodies of pegmatite and aplite are locally abundant and vary in the nature of contact with the host porphyritic quartz monzonite from diffused and gradational to very sharp and well

defined. Most commonly pegmatite and aplite occur separately, but

in a few places aplite is situated centrally in bodies of

pegmatite and is transitional with the pegmatite.

Bodies of white to cream-colored pegmatite were not observed

to exceed 12 feet in thickness and, in all cases, were continuous

through the outcrop. Crystals of microcline and microcline-

microperthite as much as 2% inches in length are common. Also

identifiable megascopically are quartz, black tourmaline, and,

in some pegmatite, red garnet.

Microscopically, the pegmatite is composed essentially of

quartz, microcline and microcline-microperthite, and sodic

plagioclase. Quartz occurs as anhedral grains interstitial to all

other minerals. Microcline and microcline-microperthite, comprising

as much as 58 percent of the rock, are euhedral to subhedral, 115

show grid structure, and commonly enclose particles of plagio­ clase, Plagioclase is alblte-oligoclase (An^j^) , which shows albite twinning* It comprises as much as 15 percent of the pegmatite and is not sericitized* Euhedral tourmaline, as much

as 6 mm in length, is pleochroic in light yellow to olive or blue

and is, in in some specimens, partly altered to biotite and chlorite*

Some of the larger crystals of tourmaline are fractured. Euhedral garnet, averaging 3 mm in diameter, is fractured and partly

altered to biotite and chlorite along fractures in some specimens*

Biotite, pleochroic in light yellow to olive, occurs as a minor alteration of both tourmaline and garnet. Pale green chlorite

is also secondary after those two minerals. Euhedral apatite is

ubiquitous.

Aplite bodies are massive, white to pink, and fine grained

and saccharoidal in texture. Quartz and feldspar are hardly

recognizable, but tourmaline and garnet are conspicuous in hand

specimen. Most aplites are less than four feet in thickness.

In thin section the aplite is compositionally quartz monzonite,

and the essential minerals are quartz, plagioclase, and microcline.

Quartz is generally anhedral and interstitial to other minerals and

makes up as much as 23 percent of the aplite. Unsericitized anhedral

albite-oligoclase (An^..^) exhibits albite twinning and com­

prises as much as 43 percent of the rock. Microcline and 116 microcline-microperthite, as much as 25 percent of the rock, show grid structure and commonly inclose plagioclase. Euhedral tourmaline, pleochroic in pale yellow to blue, is present in the quartz matrix and is included in both types of feldspar. Euhedral garnet as much as 0.80 mm in diameter is widely disseminated throughout the rock. Isolated small flakes of muscovite are present in a few thin sections. Euhedral apatite is included in quartz and feldspar.

Approximate modal analyses of the porphyritic quartz monzo- nite, diorite inclusions, pegmatite, and aplite are given in

Table 6.

Exeter diorite

General statement

The Exeter diorite was named by C. H. Hitchcock (1877, part 2, p. 658-695) for exposures in Exeter township, New Hampshire.

More detailed studies of the diorite were made by Johnson (1936,

30 pp.) in the Dover 15-minute quadrangle, and by Freedman

(1950, p. 464-465) in the M t . Pawtuckaway quadrangle. Other studies of the Exeter diorite were made by Katz (1917, p. 176) and Meyers (1940, p. 33). Billings (1956, p. 65-66, 112, 129, 141) summarized previous investigations. Although Johnson classified 117 the body as a granodiorite, the writert on the basis of extensive microscopic study, concurs with Billings that the dominant single lithologic type of the pluton is diorite.

The Exeter diorite pluton occupies most of the core of the

Exeter anticline and is approximately 20 miles long and varies in width from 0.5 mile, where the Cocheco River passes through Dover,

to 4.5 miles in the southern part of Durham township. The pluton

trends northeast-southwest through the townships of Rollinsford,

Dover, Madbury, Durham, Newmarket, Newfields, Exeter, and Brentwood

in the Dover quadrangle. Additionally, the Exeter diorite occurs

in the southeast portion of the Ht. Pawtuckaway quadrangle to the west, and the northeast portion of the Haverhill quadrangle to the

southwest. The Exeter pluton conforms regionally to the trend

of the intruded metamorphic rocks, but locally crosscutting relation­

ships prevail.

In addition to the main mass of the Exeter pluton, eight

smaller bodies of diorite were mapped, some of which were noted

by Katz (1917, p. 176), Meyers (1940, p. 33), and Billings

(1956, p. 66). The largest of these relatively small areas of

diorite, which are in Stratham, Greenland, Hampton, Hampton Falls,

North Hampton, Exeter, Kensington, and Seabrook townships, attains

a maximum length of 1-3/4 miles and a width of \ mile. As shown

on the accompanying geologic map, the diorite bodies extend in a

disconnected train from Greenland to Seabrook, New Hampshire. 118

Because of the striking lithologic and structural similarity and the geographic distribution of the smaller diorite bodies, the writer believes they are genetically related to the main

Exeter diorite mass and therefore they are included in the dis­ cussion of the Exeter diorite. Although the southernmost diorite body is close to the Newburyport quartz diorite, the lack of a primary foliation, everywhere present in the Newburyport quartz diorite, and the general paucity of quartz, further suggest an affinity with the Exeter pluton. It is also possible, however, that the Exeter pluton, the satellitic diorite bodies, and the

Newburyport quartz diorite are all related to a common magmatic source, with the observed lithologic and structural differences due to a combination of magmatic differentiation and a separa­ tion in the time of emplacement.

Metamorphism attributable to the Exeter diorite extends no more than a few tens of feet in the host Kittery and Eliot for­ mations. Most inclusions are sharply defined and only rarely show any evidence of assimilation by the diorite. Inclusions and contact rocks of the hosts have been elevated to the albite- epidote-hornfels facies of contact metamorphism, for the most part; a few inclusions, however, exhibit mineralogy of the horn­ blende hornfels facies. 119

Although Inclusions of the Kittery and Eliot formations are not are, they are especially abundant in the southern part of

the Exeter pluton 0.25 mile south of South Side State Road, 1.50 miles northwest of Exeter. At that locality a large area of

Kittery formation is surrounded by diorite and is extensively

penetrated by thin dikes of the diorite. This occurrence of

Kittery formation may represent either a stoped and foundered

block or a roof pendant.

The southernmost satellitic body of diorite is also laden

with Inclusions. There fragments of the Eliot formation are

present in such abundance that each outcrop contains at least one

inclusion.

Most inclusions, particularly those of the Eliot formation,

exhibit foliation and, in some instances, small folds, which

suggests that metamorphism and deformation had preceded, at least

in part, the emplacement of the Exeter diorite.

The Exeter pluton shows a gradational change in composition

from gabbro in the southwest to diorite and quartz diorite

centrally and to quartz monzonite in the northeast, as determined

from microscopic study. Diorite is the dominant rock type,

however, and local deviations from the general trend of compo­

sitional change are also present. Many aplite dikes and a few

granite dikes are also present in the diorite bodies and the

Exeter pluton, none of which exceed one foot in thickness. 120

The change In Che Exeter pluton from mafic to silicic as one proceeds northward, In addition to the large area of inclusion west of Exeter and the relative paucity of inclusions north of Durham, suggest that perhaps the intrusion of the diorite penetrated higher into the earth's crust at its northern end than at its southern end. If this were true, erosion could then expose part of the roof of the metamorphic rock chamber and some of the more mafic earlier crystallized rocks of the pluton in the southern area, and more silicic differentiated igneous rocks in the north.

Rocks of all the diorite bodies are massive, with one exception. Those at Sawyers, one mile south of Dover, are strongly sheared parallel to the contact with the Kittery formation.

The deformation may be either syntectonic or post-tectonic.

Stresses due to regional deformation concomitant with emplacement of the diorite could have produced shear zones locally and marginally. Regional or local deformational stresses postdating the emplacement of the diorite could also have been responsible for marginal shearing of the diorite. Unfortunately, no thin sections were made of rocks from this area.

Consistent jointing in the diorite bodies is generally absent,

consequently few structural data are indicated on the map for the

Exeter diorite. 121

Inasmuch as several lithologic types comprise the Exeter diorite bodies, each is discussed individually below. Repre­ sentative approximate modal analyses of rocks of the Exeter pluton and the smaller diorite bodies are given in Table 7.

Gabbro

Rocks of the gabbroic facies of the Exeter diorite are

exposed in the Exeter pluton in Exeter township and, to a very

limited extent, in Newfields and Newmarket townships, and in the margins of the two smaller diorite bodies on the Exeter-Hampton

and Greenland-Stratham town boundaries. Megascopically the

gabbro is massive, dark gray, dark green, or black, coarse

grained, and equigranular. Conspicuous minerals in hand specimen

are pyroxene and amphibole, as much as 7 mm in length, biotite

and chlorite as much as 8 mm in width, and plagioclase as much as

4 mm in length.

Microscopically the gabbro is hypidiomorphlc granular and

contains as essential minerals plagioclase, pyroxene (both hyper-

sthene and augite), and uralitic amphibole.

Andesine-labrador!te (Axl43 „54) comprises as much as 65 percent

of the rock and Is commonly serlcitized or saussuritized, perhaps

deuterically, to albite (An^)), epidote-zoisite, and sericite. 122

Albite twinning in the plagioclase feldspar is ubiquitous where it is not obscured by alteration products. The pyroxene group is represented by hypersthene and augite. Hypersthene is ple- ochroic in pale pink, shows parallel extinction, and is commonly rimmed by augite. Schiller structure appears in much of the hypersthene. Augite is colorless and subhedral. Both pyroxenes are altered, at least in part, to uralite, biotite, or chlorite.

Hypersthene and augite make up as much as 67 percent of the gabbro.

Uralitic amphibole, which is present as an alteration of both

types of pyroxene described above, is pleochroic in light to medium green. Most is fibrous, and many specimens exhibit relict

schiller structure inherited from pre-existent hypersthene.

Uralite generally comprises no more than 15 percent of the rock,

but in one thin section it makes up approximately 70 percent.

Of the minor constituents of the gabbro, biotite, which is

pleochroic in light yellow to dark brown, occurs as an alteration

of amphibole or pyroxen and is itself partly altered to chlorite.

Biotite flakes commonly contain rutile needles, magnetite blebs,

apatite prisms, and, in a few specimens, unaltered fragments of

pyroxene.

Accessory minerals of the gabbro include a few interstitial

quartz grains; epidote laths, needles, and grains in feldspar and

quartz; and euhedral to anhedral magnetite, which is disseminated

throughout the rock. Apatite prisms occur in feldspar and quartz.

Sericite is present as an alteration of feldspar. 123

Diorite

Massive diorite, the most abundant single rock type in the

Exeter diorite bodies, ranges from medium to dark gray and medium to coarse grained. Megascopically identifiable are light gray to light gray-green plagioclase as much as 3 mm in length, black pyroxene as much as 2 am in length, green-black amphibole as much as 4 am in length, dark-brown biotite to 1 mm, and some dark- green chlorite.

Microscopically, plagioclase ranges from oligoclase to andesine (Ano5^/|/|) , with the labradorite occurring as the central areas of noraxally zoned crystals. Albite twinning is common to all plagioclase grains. In a few thin sections the plagioclase shows bent and fractured twin lamellae, suggesting that it was subjected to stress during or after emplaceoient of the diorite bodies. All specimens of plagioclase are heavily sericitized and enclose hornblende partly altered to biotite, pyroxene, magnetite, and apatite. Some myrmekitic Intergrowth of plagioclase with quartz was observed.

The pyroxene group is represented by both hypersthene and augite. Hypersthene occurs as anhedral cores in augite and amphibole. It is generally pleochroic in colorless to pale green or pink and commonly shows schiller structure. Augite is generally anhedral and colorless, and surrounds cores of hypersthene. Anhedral blebs of magnetite and euhedral prisms of apatite are coamon inclusions. Pyroxene comprises as much as 32 percent of the diorite. 124

The amphibole la In most specimens uralltlc hornblende derived from the alteration of pyroxene, although some hornblende may be primary In origin. It generally exhibits colorless to pale green pleochroism, Is partly altered to biotite, and encloses fragments of unreplaced pyroxene, plagioclase feldspar, and euhedral apatite prisms. Amphibole attains a maximum of 25 percent in one thin section.

Of the minor components of the diorite, biotite, pleochroic in light yellow to dark red-brown, occurs as an alteration of pyroxene and amphibole. It encloses relict fragments of pyroxene and hornblende, euhedral prisms of apatite, irregular grains of zircon with pleochroic haloes, plagioclase feldspar fragments, and acicular rutile. In one specimen it makes up 18 percent of the rock.

Chlorite, which is prochlorite and penninite as indicated by their respective interference colors, is the common alteration product of biotite, amphibole, and pyroxene. It also is present in fractures in plagioclase feldspar.

Interstitial microcline-microperthite is generally absent or is present as a very minor constituent of the diorite but does rarely make a maximum of 16 percent. Most conxnonly the potassic feldspar grains are marginal to plagioclase and exhibit myrmekltic intergrowth at the contact with the plagioclase. 125

Quartz, which occurs as interstitial grains in the diorite, was not observed to exceed 6 percent of the rock.

Among the minor accessories are epidote-zoisite, sericite, magnetite, sphene, carbonate, and hematite. Epidote-zoisite apr ars primarily as an alteration of plagioclase feldspar and pyroxene but some euhedral to anhedral grains are also present in biotite and chlorite. Sericite is secondary after plagioclase.

Magnetite in irregular grains is disseminated throughout the rock, but is most conspicuous in pyroxene, amphibole, biotite, and chlorite. In several instances magnetite appears to be an exso­ lution product of those minerals. Some grains of magnetite have been altered to hematite and limonite. Sphene ranges from euhedral to anhedral and is distributed throughout the rock; some grains contain magnetite cores. Apatite prisms and needles are ubiquitous. Zircon, auhedral to anhedral, is enclosed in most other minerals; in biotite and chlorite, pleochroic haloes surround the grains. Carbonate, present in few thin sections and in very minor amounts, is an alteration of plagioclase feldspar. 126

Quartz diorite

Although quartz diorite is volumetrically a relatively minor

lithologic type in bodies of the Exeter diorite, it was identified

from the southern part of Durham township, from Durham Point, and

from three of the smaller diorite masses* Megascopically it is

nearly identical to the above described diorite in color,

texture, and mineralogy, with the exception of identifiable quartz

grains.

Microscopically, quartz comprises as much as 25 percent of

the rock and occurs as subhedral to anhedral interstitial grains.

Plagioclase, which ranges from oligoclase to andesine (An29„42^»

is slightly to moderately sericitized and comprises up to 59 percent

of the quartz diorite. All observed plagioclase shows albite

twinning and some grains exhibit myrmekitic intergrowth with

quartz. Other alteration products of plagioclase are anhedral

epidote-zoisite grains and inconspicuous amounts of carbonate.

Hornblende, pleochroic in pale green to blue green, appears

to be partly an alteration of pyroxene and makes up as much as

10 percent of the quartz diorite. Much of the hornblende is

altered to red-brown biotite which, in turn, is partly altered to

chlorite. Biotite comprises as much as 20 percent of the rock and

chlorite as much as 14 percent. Some biotite flakes are unrelated 127 to amphibole and are considered primary. Chlorite Is, In all specimens, a derivative of biotite and shows the ultrablue interference colors of penninite.

Microcline-microperthite generally makes up less than

10 percent of the rock, but in one specimen comprises 17 percent.

Grid patterns are evident in all the potassic feldspar grains.

Among the minor accessory minerals are sericite and epidote- zoisite, both of which are most commonly alterations of plagio­ clase feldspar. Some epidote-zoisite grains are apparently secondary after amphibole and some anhedra occur in biotite and chlorite.

Magnetite and hematite are randomly distributed in the rock but are somewhat more concentrated in biotite and chlorite.

Euhedral prisms and needles of apatite are included in quartz, plagioclase, and biotite. Subhedral to anhedral zircon grains are distributed throughout the rock and have created pleochroic haloes

in biotite and chlorite. Subhedral to anhedral sphene was

observed in many of the other minerals. 128

Quartz monzonlte

Quartz monzonlte was Identified from the Dover and Rollinsford areas of the Exeter pluton, and from minor dikes in other areas.

Megascopically it is somewhat similar to the quartz diorite described above. It is coarse grained, equigranular, massive, and light to medium gray.

Microscopically, quartz occurs as Interstitial grains and as

thin veinlets. In some thin sections undulatory extinction is prominent. Quartz constitutes as much as 22 percent of the rock.

Plagioclase ranges from albite to oligoclase (An^.j^) and is

slightly serlcitized in all observed specimens. In thin sections

from the Mt. Pleasant area, Dover, plagioclase shows bent and

fractured twinning planes. In other sections plagioclase and

quartz are myrmekitically intergrown. Plagioclase comprises as much as 47 percent of the quartz monzonlte.

Microcline-microperthite, which accounts for as much as

27 percent of the rock, exhibits grid structure and Carlsbad

twinning. In a few thin sections plagioclase fragments, optically

continuous, were observed in microcline. Microcline from the

Mt. Pleasant area also shows warping and fracturing. Fractures

are commonly healed by veins of unstrained quartz. Also Included

in the microcline are quartz and biotite. 129

The principal mafic mineral of the quartz monzonlte Is biotite, which is pleochroic in yellow to dark brown. It encloses grains of quartz, magnetite, and relict fragments of amphibole.

A common alteration of biotite is chlorite, which displays the ultrablue interference colors of penninite. Biotite averages

8 percent and chlorite 3 percent of the quartz monzonlte.

Neither pyroxene nor amphibole are present in quantity. In a very few specimens twinned and nonpleochroic augite makes up as much as 3 percent of the rock. Amphibole, where present, is ple­ ochroic in light to olive green and is most commonly altered to biotite; it also encloses particles of plagioclase.

Of the minor accessory minerals, epidote-zoisite and sericite occur as secondary products after plagioclase. Magnetite anhedra are disseminated throughout the rock, but are somewhat more concentrated in the secondary products of pyroxene, amphibole, and biotite. Apatite needles and prisms are present in nearly all other minerals, as are euhedral to anhedral grains of zircon. The

latter have created pleochroic haloes in biotite and chlorite.

Sphene is commonly associated with pyroxene, amphibole, and

biotite. In one thin section a crystal of black tourmaline was

observed. 130

Granite and aplite dikes

Many granite and apllte dikes occur in both the Exeter pluton and the smaller diorite bodies, but none of the dikes exceeds two feet in thickness. The granite dikes generally contain only a very few percent of mafic minerals. Most granite dikes are gra­ dational with the host rock or are separated from it by a thin selvage of aplitic material, in which case there is a marked change in texture. All granite dikes observed in the field are pink, massive, and medium to coarse grained.

Aplite dikes are in sharp contact with the host Exeter diorite, and differ strikingly in color and texture. The aplite dikes are quartz monzonlte mineralogically. These dikes are light pink, both where fresh and weathered, and the texture is saccharoidal and fine grained.

The observed field occurrence of both the granite and aplite dikes suggests that both are late magmatic phenomena, the granite dikes perhaps in situ products of crystallization of residual solutions of the original magma, and the aplite dikes perhaps late- stage injections of similar magmatic material from a residual subjacent source along zones of weakness or early-formed joints.

Most granite and aplite dikes occur in the gabbro to quartz diorite facies of the Exeter bodies. None of the dikes, granite or aplite, is foliated. 131

Microscopically, Che major constituents of the granite dikes are subhedral microcline-microperthite and plagioclase, and anhedral quartz. In all specimens studied, microcline displays a grid pattern and is intergrown with, and has perhaps partly replaced, plagioclase. Microcline ranges from 47 to 63 percent of the granite. Albite to oligoclase (An^ . . ^ ) » makes up as much as 20 percent of the rock and shows albite twinning in nearly all specimens. Common alteration products are sericite and epidote- zoisite. Unstrained grains of quartz are interstitial to the feldspar and comprise as much as 53 percent of the granite.

Accessory minerals are biotite, pleochroic in yellow and light brown, and chlorite, which is pleochroic in light green and exhibits ultrablue interference colors. Chlorite appears to have been secondarily derived from biotite. These two minerals total a maximum of 3 percent of the granite.

Minor accessory minerals of the granite are sericite, epidote- zoisite, apatite, sphene, magnetite, and muscovite.

Microscopically the aplite dikes are composed chiefly of plagioclase, microcline, and quartz. Plagioclase, which is domi­ nantly oligoclase * is slightly altered to sericite and epidote-zoisite and encloses euhedral apatite. In some thin sections plagioclase amounts to as much as 52 percent of the aplite. 132

Microcline shows a grid pattern in all sections and constitutes as much as 39 percent of the rock. Quartz, as much as 23 percent, occurs as anhedral grains interstitial to the feldspar.

Among the minor accessory minerals is biotite, which occurs as flakes and tablets pleochroic in yellow-brown to dark olive.

It is conanonly included in plagioclase, microcline, and muscovite.

Chlorite, pleochroic in light green, generally is present as an alteration of biotite. Sericite and epidote-zoisite are very minor alteration products of plagioclase. Other minerals present are apatite, magnetite, muscovite, and zircon.

Quartz monzonite

An irregularly shaped body of quartz monzonite, which is part of a pluton more extensively developed in the Mt, Pawtuckaway quadrangle on the west, crops out in the northwest corner of the

Dover quadrangle in Dover, Rochester, and Barrington townships.

That part of the pluton in the Dover quadrangle has been reported by Katz (1917, p. 177) as granite, and by Meyers (1940, p. 33) as a granite perhaps correlative with the Biddeford granite of

southwestern Maine. Freedman (1950, p. 466) described that part of

the pluton in the Mt. Pawtuckaway quadrangle. Billings (1956, p. 66-67) included the quartz monzonite in the large granitic

Fitchburg pluton which extends from Worcester, Massachusetts to

Somersworth, New Hampshire. 133

Although Freedman (1950, pi. 1) showed, in the northeast part of the Mt. Pawtuckaway quadrangle, a body of quartz diorite which, by the trend of its contact, should also be present in the

Dover quadrangle, the writer found no evidence of quartz diorite, only quartz monzonite and pegmatite. In the southeast corner of

the Alton quadrangle, which is northwest of the Dover quadrangle,

Stewart (1961, p. 19) reported biotite granite. Perhaps the complexity of the Fitchburg pluton is the reason for the dis­ crepancies mentioned above.

Excellent exposures of the quartz monzonite and its related pegmatite are present on Green Hill, Barrington, and on the banks of

Isinglass River at a position on the map that is southeast of the

first "R" in ’’Rochester". Although the contact of the quartz monzonite with the Berwick or Littleton formations was not observed

in the field, stringers of silicic igneous rock, up to two inches

in width, were seen in the Berwick outcrops nearest the quartz monzonite, and pegmatite bodies similar to those in the quartz monzonite were seen in contact with the Littleton formation.

Additional support for the idea of intrusion of the quartz monzo­ nite into the Berwick and Littleton formations lies in the fact

that the grade of the metamorphic rocks is highest in areas close

to the quartz monzonite and diminishes eastward through the

Littleton formation, Berwick formation, and part of the Eliot

formation. 134

The quartz monzonite, as observed in the Dover quadrangle, is light gray to buff, medium to coarse grained, equigranular, and massive. The rock is light gray on weathered surfaces.

Pegmatite is rarely absent from exposures of the quartz monzonite.

In hand specimens of the quartz monzonlte, potassic feldspar, plagioclase, quartz, muscovite, biotite, and garnet are identifi­ able. Limonite stain is common on fracture surfaces.

Essential minerals are plagioclase, microcline and microcline- microperthite, and quartz. Albite-oligoclase comPrises between 31 and 38 percent of the rock. It generally shows albite twinning and, more rarely, Carlsbad twinning, and is most commonly subhedral and slightly sericitized. Myrmekitic intergrowths with quartz were observed in some thin sections. Microcline and microcline-microperthite constitute as much as 31 percent of the rock and exhibit a grid structure under the microscope. Some biotite is poikilitically included. Quartz constitutes as much as 28 percent of the rock and is anhedral and interstitial to the feldspars.

Biotite was observed in some specimens, but makes up no more than 6 percent of the rock. It is pleochroic in light brown to dark red-brown and contains euhedral prisms of apatite and euhedral to subhedral grains of zircon surrounded by pleochroic haloes. Biotite is commonly altered, at least in part, to chlorite. 135

Chlorite Is present only as an alteration of biotite, and is pleochroic in light green. Interference colors of ultrablue suggest a penninitic variety. Garnet, though common, is not ubiquitous. Where present, it is euhedral to subhedral and pale pink in ordinary light. Muscovite flakes, undeformed, were noted in almost all thin sections.

Minor accessory minerals include euhedral apatite, grains of magnetite, and euhedral to anhedral zircon.

Pegmatite bodies in the quartz monzonite, at different places, display both sharp and gradational contacts with the host. In many exposures pegmatite is volumetrically much greater than the quartz monzonite. Potassic feldspar crystals up to eight inches and garnet crystals or aggregates to three inches were observed.

Other minerals identified are quartz, plagioclase, biotite, and muscovite. Graphic granite is very comaon in the pegmatite bodies.

No thin section studies were made of the pegmatite; approx* imate modal analyses of the quartz monzonlte are given in Table 7. 136

White Mountain Plutonic-Volcanic Series

General statement

The name White Mountain magma series was introduced by

Billings (1935, p. 28) to designate a series of comagmatic volcanic and plutonic rocks of probable Mississippian(?) age.

It was later reclassified by him as a plutonic-volcanic series

(Billings, 1956, p. 69). Characteristically, rocks of the

White Mountain series show alkaline affinities, are primarily massive, and postdate regional metamorphism in New Hampshire.

In the Dover-Exeter-Portsmouth region, the White Mountain

series is represented by many camptonite dikes and sills and a single gjranophyre dike.

C a m p t o n i t e

Although dikes and sills of camptonite occur throughout the area mapped, they seem to be more abundant east of the Exeter pluton. Thicknesses of camptonite bodies range from less than

one inch to more than 20 feet. Multiple dikes and sills were observed

in several localities. All camptonite bodies display narrow chilled margins against the host rocks and have not observably contributed

to the metamorphism of the enclosing rocks. 137

Forcible rather than permissive emplacement of the camptonite bodies in some places is indicated by the presence of many inclusions of the host rock and by the dilative nature of some of the dikes and sills. Plate XIII shows crosscutting camptonite bodies and dilated country rock. A contour diagram showing the orien­ tation of 181 camptonite dikes and sills is given in Figure 2.

Megascopically, the camptonite is dark green to black, generally aphanitic to fine-grained phaneritic, with a few specimens medium grained and ophitic. A porphyritic texture is common. Stout black pyroxene crystals and laths of plagioclase as much as 5 mm long comprise the majority of phenocrysts; hornblende phenocrysts are

locally abundant. Weathered surfaces of the camptonite are black or rusty brown.

Microscopically the camptonite bodies are ophitic, with essential minerals labradorite (An ), titanaugite, and, in some of the 50—67 rock, barkevikite. Serpentine, probably deuteric in origin, is

common. Groundmass minerals range from 0.013 min to 0.70 mm and phenocrysts from 0.305 mm to 4 mm. Labradorite occurs as laths, most of which show albite twinning and slight to moderate sericiti-

zation. In those specimens in which two generations of labradorite

are present, the younger and smaller interstitial laths exhibit a

lesser degree of sericitization. Normal zoning is present in some

plagioclase, particularly the larger crystals. 138

PLATE XIII

Camptonite dikes in the lower member of the Rye formation.

Crosscutting dikes that contain inclusions of metamorphic rocks and that dilate the host rocks. Rye North Beach„ Rye, New

Hampshire. 1 3 9

/■-'

Figure 2.— Contour diagram of camptonite dikes and sills.

Poles of perpendiculars plotted on lower hemisphere of equal area net. One hundred eighty-one readings. 140

Titanaugite Is pleochroic in light to medium pink, euhedral to subhedral, as much as 2.5 ran in length, and is zoned in some speci­ mens. Twinned crystals are not uncommon. Alteration, probably deuteric, is to serpentine.

Barkevikite, pleochroic in light to dark brown, occurs as euhedral phenocrysts and as Interstitial needles associated with labradorite and titanaugite. Pseudo-hexagonal dark-brown biotite crystals are also common as microscopic phenocrysts.

Serpentine, composed of antigorite and chrysotile, was observed in nearly all sections. Although no idiomorphic pseudomorphs of olivine were distinguishable, the possibility exists that the serpentine is an alteration product, in part, of pre-existent olivine.

Some serpentine was derived from alteration of titanaugite, however.

Of the accessory minerals, magnetite was observed in titan­ augite and biotite, and associated with serpentine and chlorite, ranging from euhedral to subhedral. Apatite, in euhedral prisms, occurs in labradorite, biotite, and chlorite. Chlorite is present as an alteration of biotite, and is pleochroic in pale green. Epidote- zoisite occurs as an alteration of pyroxene and, to a lesser degree, labradorite. Sphene is present as irregular grains associated with magnetite and serpentine. An unidentified carbonate, probably calclte, may represent a deuteric alteration of earlier calcium- bearing minerals. It is associated with labradorite, epidote, and serpentine. Sericite is present as an alteration of labradorite. 141

Thin section study of two sets of multiple dikes has Indicated a trend toward decreasing alkalinity from older to younger camptonite bodies as evidenced by a smaller percentage of tltanaugite and barkeviklte.

Estimated modal analyses of camptonites are given in Table 8.

Granophyre

The sole dike of granophyre found in the area is exposed in a road cut 1.37 miles southeast of Newington Station, Newington. The body is about three feet wide and has chilled margins. On fresh surface the rock is cream to light gray and exhibits conspicuous clear quartz blebs, feldspar, and pyrite.

Microscopically the granophyre consists of a cuneiform inter* growth of quartz and mlcrocline, which constitute approximately 91 percent of the rock. The mlcrocline portion shows Carlsbad twinning and is slightly altered to a kaolinitic(?) material. Accessory minerals are sphene in irregular grains, epidote, calcite, pyrite that has been altered to hematite and limonite, and ilmenite that is partly altered to leucoxene. Grain sizes vary from .019 mm to

0.30 mm. STRUCTURAL GEOLOGY

General Statement

The major structural trend of rocks in the Dover-Exeter-

Portsmouth region is northeast, reflecting the trend of the prominent folds, which are, from southeast to northwest, the Rye anticline, the Great Bay syncline, and the Exeter anticline.

The strike of the one fault mapped also conforms generally to the regional trend. Intrusive igneous rocks of the Hillsboro and

White Mountain plutonic series are also an integral part of the northeast-striking system, inasmuch as they are for the most part

concordant.

Foliation, minor folds, lineations, and joints are abundantly

displayed throughout the area.

According to Billings (1956, p. 53), the major rock defor­ mation in New Hampshire occurred during the middle to late Devonian

Acadian orogeny. The major folding, faulting, regional metamorphism,

and the emplacement of rocks of the Hillsboro plutonic series are

considered to have taken place at that time. The intrusion of rocks

of the White Mountain plutonic series probably occurred during the

Mississippian period.

142 143

Folds

General statement

Folds of southeastern New Hampshire are considered by Billings

(1956, p. 112) to be part of the northeast-trending Rockingham

anticlinorium, which is approximately 15 miles wide from the sea-

coast westward to the Fitchburg pluton in the vicinity of Nottingham,

New Hampshire, in the Mt. Pawtuckaway quadrangle. The northeast-

trending major folds of the anticlinorium in the Dover-Exeter-

Portsmouth region are the Rye anticline, the Great Bay syncline,

and the Exeter anticline.

Rye anticline

Located in the coastal area of New Hampshire, the Rye anticline

extends from Gerrish Island, Maine, to the Newburyport quartz

diorite intrusive in Seabrook, New Hampshire, a distance of about

16^ miles. It is probably overturned to the southeast, contains a

core of the Rye formation, and is flanked on the south and west by

the Kittery formation. Linear elements, which were observed in the

field in both the Rye formation and the contiguous Kittery formation

and plotted on the map, strongly suggest a gentle southwest plunge

for the Rye anticline in most of coastal New Hampshire. A few

structural data, however, from the north of New Castle, indicate a

reversal in plunge from southwest to northeast, making the Rye 144 anticline a doubly plunging structure. The preponderance of steep northwest dips of both bedding and foliation indicate that the

Rye anticline is slightly overturned to the southeast. The presence of many minor folds overturned In the same direction as the postulated Rye anticline tends to support this hypothesis.

Great Bay syncline

Bordering the Rye anticline on the west is the northeast- trending Great Bay syncline, which appears to be slightly overturned to the southeast; the central portion is occupied by the Eliot formation. Although Billings (1956, p. 112) placed the axial trace of the syncline near Newington, Stratham, and 2 miles east of Exeter, the writer is of the opinion that the sparseness of exposures of the

Eliot formation and of the necessary structural data preclude an accurate establishment of the axial trace. Further difficulty regarding an analysis of the Great Bay syncline is the presence of anomalous structural data from the Kittery and Eliot formations on the Newington shore of Great Bay east of Durham township, possibly resulting from a northeast-southwest shearing action during the period of regional deformation and intrusion.

It appears to the writer that rocks of some parts of the Great

Bay syncline must have been more deformed than others, because of

the somewhat irregular widths and hour-glass map pattern of the

syncline between the Rye and Exeter anticlines. 145

Exeter anticline

The central part of the Exeter anticline, which is west of the

Great Bay syncline, is almost completely occupied by the Exeter pluton and may be overturned to the southeast. Although sufficient structural data were not obtained from the rocks surrounding the

Exeter pluton, the existence of Kittery formation in contact with the intrusive on the east and on the west, and the presence of the younger Eliot formation bordering the Kittery formation on both sides of the pluton, indicate that the structure is anticlinal.

Not all the metamorphic rocks west of the axis of the Exeter anticline are considered to be repetition of strata present east of the anticline, inasmuch as the maximum width of the area of outcrop of the infolded Eliot formation in the Great Bay syncline is 5 miles and the combined width of the homoclinal Eliot and Berwick formations west of the anticline is also 5 miles. The segment of Littleton

formation on the east margin of the quartz monzonite has no

correlative east of the Exeter anticline. 146

Faults

General statement

Only two major faults have been mapped In the Dover-Exeter-

Portsmouth region* One is indicated on the accompanying map in the vicinity of Portsmouth (Plate I), the other, shown by Billings (1P55) on the geologic map of New Hampshire, in Seabrook, is not shown for reasons discussed below*

Portsmouth fault

A fault contact between the Rye and Kittery formations was mapped for a distance of approximately 9 miles from northwest New

Castle to North Hampton. On Lafayette Road (U* S. Route 1) at the west end of Sagamore Hill, Portsmouth, are outcrops showing highly

contorted and somewhat brecciated rocks of the Kittery formation and

two minor faults of undeterminable displacement. Both fault zones,

2 to 3 feet wide, dip very steeply to the west and consist of rubble

heavily stained by limonite* The main fault or faults are therefore -> considered to dip steeply to the west. In the summer of 1953, minor

drag folds related to the faults and exposed in the fault zones

indicated that the east sides of the faults moved up*

On the southeast shore of Goat Island, New Castle, and in out­

crops on the east end of Brumble Hill, North Hampton, are exposures of

brecciated and partly silicified Kittery formation. 147

There is no topographic evidence for the fault in the area mapped. Although metamorphic zones are apparently not displaced because of the fault, the presence of concordant foliated and granulated Breakfast Hill granite only in the Rye formation and near the Kittery formation contact supports the hypothesis of a fault developed during the Acadian period of orogeny, along which deeply buried and intruded portions of the Rye formation were elevated.

Because of the deduced conformable stratigraphic relationship between the Rye and Kittery formations outside the fault zone in

North Hampton and Hampton, and because of the nature of the movement on the two minor faults described above, the writer concludes that movement on the Portsmouth fault, of unknown displacement and attitude, caused relative elevation of the east side and depression of the west.

Seabrook thrust

No evidence was seen in the field for a fault contact between the Newburyport quartz diorite and the metamorphic rocks on the north in Seabrook, New Hampshire, as described by Billings (1956, p. 118). He considered the Newburyport quartz diorite to be probably

Precambrian in age and unconformably below the stratigraphic units of southeastern New Hampshire. The absence of the oldest of the metamorphic rocks in the area, the Ordovician(?) Rye formation, therefore suggested a fault to him. The writert on the other hand, relates the Newburyport quartz diorite to the Devonian(?) Hillsboro plutonic series, in which case a fault contact with the Silurian(?) metamorphic rocks on the north is unnecessary. The intrusive breccia of Bound Rock, on the Seabrook coast, which was cited by Billings as evidence of a fault contact, is discussed by the writer with the Newburyport quartz diorite as a near-contact outcrop of the intrusive rock that contains abundant dark-colored autoliths. Moreover, map data indicate a parallel to subparallel relationship between the foliation of the quartz diorite and the foliation and bedding of adjacent metamorphic rocks.

Minor structural features

General statement

In addition to the major folds, faults, and intrusive masses,

several types of minor features in the metamorphic rocks contribute

to the analysis of the bedrock geology of southeastern New

Hampshire. Among these are minor folds, cleavage, schistosity,

lineation, and joints. 149

Minor folds

Superimposed on all the major folds of the area are many minor

folds which, in most cases, reflect the attitude of the larger

folds. Plunges of the minor fold axes are generally parallel to

those of the major folds and to other linear elements. Observed

amplitudes of minor folds range from microscopic to approximately

10 feet. The majority of folds are overturned to the southeast

and exhibit axial planes and fold limbs which dip steeply to the

west. In a few outcrops minor folds may be properly designated

isoclinal.

Exceptions to the correlation between major and minor folds

exist east of the Exeter pluton from the vicinity of Cedar Point,

Durham, south along both sides of the entry to Great Bay. In

this area strikes and dips of bedding and cleavage, and the

strikes of fold axes, depart from those more comnonly observed.

The erratic local structures may be the result of a couple

exerted during deformation or of distortion caused by forcible

intrusion of subjacent portions of the Exeter pluton. In support

of the latter hypothesis is the presence of metamorphic rocks of

biotite grade at Fox Point and Adams Point, a mile or more east

of known outcrops of Exeter diorite, which in general caused little

metamorphism except at its contacts with the host rocks. 150

Some thickening and thinning of folded beds was observed , particularly in the Eliot and Kittery formations in the chlorite

zone. At Cedar Point on Little Bay are excellent exposures of

folded interbedded quartzose and slaty rocks, in which the quartzose

strata have maintained a uniform thickness, and in which the slaty

beds have been thinned on the fold limbs and thickened on crests

and troughs.

Cleavage

Both axial plane cleavage and fracture cleavage are well

exhibited in the chlorite zones of the Kittery and Eliot formations.

In all exposures observed, cleavage in folded argillaceous beds is

parallel to the axial planes. In argillaceous beds it is closely

spaced, about 1/8 inch; in the quartzose and more competent beds

it is more widely spaced, approximately % inch, and is less

rigorously defined.

Axial plane cleavage and fracture cleavage are most commonly

at high angles to bedding in the Eliot and Kittery formations. 151

Schistosity

Schistosity Is present in all metamorphic rock units in which metamorphism is above the chlorite grade, and is defined by the planar orientation of sericite, chlorite, muscovite, biotite, and amphiboles. In most rocks, but particularly in the Rye formation, schistosity is apparently parallel to bedding. This may be accounted for by isoclinal folding of the rocks, which has been observed in some places. Other possibilities, however, are that the schistosity is bedding schistosity due to flexural slipping parallel to bedding planes in the more competent beds, which seems most likely to the writer, or that metamorphic mineral development is mimetic in origin, with recrystallization occurring in directions of least stress.

In some rocks of the Kittery and Berwick formations, however, post-deformational recrystallization has resulted in unoriented biotite porphyroblasts, which are located athwart schistosity.

Lineation

For the most part, lineations in the stratigraphic units of

southeastern New Hampshire parallel minor and major fold axes and

consist of (1) intersections of cleavage and bedding in the chlor­

ite zone of the Eliot and Kittery formations; (2) trains of musco­ vite, biotite, and granulated feldspar and tourmaline; 152

(3) aligned hornblende and actinolite in the Berwick, Kittery, and

Rye formations; and (4) broad corrugations or warps in Che Rye formation which lie in the plane of foliation and reach several inches in wave length*

The broad corrugations of rocks of the Rye formation and of the syntectonic granitic intrusives that have invaded it, may be due to arcuation of those rocks during deformation* Regional flexure of the Rye formation is apparent on the map (Plate I)*

Joints

In all units but the Rye formation, the Breakfast Hill granite an£ pegmatite that have intruded it, and the eastern belt of

Kittery formation, jointing is erratic and is probably due, in a

large measure, to local control. Contour diagrams of joint

orientations in the Rye formation, the Breakfast Hill granite and pegmatite, and the part of the Kittery formation bordering the

Rye formation on the west are shown in Figures 3, 4 and 5. These

are based on equal area plots of poles to joint surfaces. 153

\ V \-i. .-a \ 'A \ *'A ‘ , • \

1 V

/ v

‘fC-'S) ■'

/ /

/ / . ' ‘ " r f

■ . . ' / / /

.'i h. i % 5 ' 8 % 8 10*/.

Figure 3.— Contour diagram o£ joints in the Rye formation.

Poles of perpendiculars plotted on lover hemisphere of equal area net. Fifty-eight readings. 154

A I

I.) -4

Figure 4.--Contour diagram of joints in the Kittery formation.

Poles of perpendiculars plotted on lower hemisphere of equal area net.

Twenty-eight readings. hemisphere of equal area net. Twenty-six readings. Twenty-six net. area equal of hemisphere rnt ad emtt. oe o predclr potd n lower on plotted perpendiculars of Poles pegmatite. and granite iue . Cnor iga o jit i te rafs Hill Breakfast the in joints of diagram Contour 5.— Figure •w 155 Concentrationso* orientations in the east-west and northeast* southwest areas of the diagrams imply a dominant north-south and northwest-southeast orientation of joints in the units investigated.

Maximum concentrations near or at the circumference indicate steeply dipping or vertical dips of the mapped joints.

Joints in the areas mentioned above may be extension joints,

or the result of arcuation during deformation that also may have produced the corrugation lineation in the Rye formation and the

Breakfast Hill granite and pegmatite. METAMORPHISM

General Statement

All the rocks of sedimentary and volcanic origin in the

Dover-Exeter-Portsmouth region have been subjected to regional metamorphism, and range in grade from the quartz-albite-muscovite-

chlorite subfacies of the greenschist facies to the sillimanite- 1 almandine-muscovite subfacies of the almandine-amphibolite facies.

Field and laboratory evidence reveals that the time of metamorphism

and that of deformation were essentially synchronous, although

there is no apparent direct relationship between intensity of

folding and the degree of metamorphism. Rather, metamorphism

seems to be related to plutonic rocks of granitic composition,

such as those in the northwest and southeast parts of the mapped

a r e a .

In general, the grade of regional metamorphism increases

gradually both northwest and southeast from the Great Bay syncline,

with but very local disruptions of the trend, mostly near intrusive

bodies of diorite, such as the one at Adams Point, in southeast

Durham, where biotite was noted in a small area. The most inten­

sive folding and crumpling occurs in the chlorite zone of the Eliot

^The facies classification of Turner and Verhoogen, 1960, is used throughout the discussion of metamorphic rocks.

157 158 and Kittery formations; folds in other units are generally less complicated. Argillaceous rocks of the chlorite zone have been converted to slates and phyllites; those of the biotite, garnet, and sillimanite zones to more schistose rock types.

Contact metamorphism has played only a small part in the reconstitution of the rocks, although the heat and possibly emanations from granitic intrusions apparently contributed much

to the localization of metamorphic zones. Effects of retrogressive metamorphism, although minor for the most part, are nevertheless present in a great many rocks* There has been some introduction

of material from extraneous igneous sources in the formation of

the injection and permeation gneiss of the upper member of the

Rye formation and in the formation of migmatitic complexes of the

lower member.

Metamorphic Zonation

Although discussion of metamorphic rock types has referred

to the facies classification, the writer has used the zonal

method of indicating metamorphic intensity on the map both for

clarity and for convenience. Shown on the map are isograds

delineating the biotite, oligoclase-actinolite, and sillimanite

zones which, in the order given, indicate increasing metamorphic

grade. Rocks on the low intensity side of the biotite isograd are 159 in Che chlorite zone. Isograds for the indicator minerals garnet, staurolite, and kyanite of the zonal classification are omitted because of the absence or paucity of those minerals, which is apparently due to the lack of rock of suitable original composition.

For this reason, Freedman's (1950, fig. 3) garnet isograd was not continued into the western part of the Dover quadrangle. In the northwest part of the map some rocks on the high intensity side of the oligoclase-actinolite isograd contain garnet and staurolite, the latter mineral occurring only in the Littleton formation.

In the southeast, in the area shown between the oligoclase- actinolite and sillimanite isograds, garnet is abundant only in rocks of the lower member of the Rye formation; staurolite is absent from all rocks in the southeastern area.

In the northwest, isograds are crudely related to the mapped border of the quartz monzonite. The southeast trend of the biotite and oligoclase-actinolite isograds east of the Exeter pluton in

Rollinsford is probably due to the metamorphic effects caused by the emplacement of the igneous rock complex that is located to the east in Maine, as shown by Katz (1917, p i . 61),

Isograds in the southeast show a close relationship to for- mational contacts, similar to the case cited by Cady (1956), which he explained as the result of differential uplift of once nearly horizontal isothermal surfaces. 160

Time of Metamorphism

Rocks of southeastern New Hampshire were metamorphosed during only one period, and the metamorphism was syntectonic for the most part, although some rocks show evidence of post-tectonic recrystallization. Metamorphism of the rocks is directly related in time to the intrusion of igneous rocks of the Hillsboro plutonic series of Devonian(?) age.

The parallelism of lineation in the Breakfast Hill granite and pegmatite with that in the adjacent rocks of the Rye for­ mation is interpreted as indicating that both underwent the same deformation. The existence of random porphyroblasts of biotite in rocks peripheral to the quartz monzonite in the northwest and in some parts of the Kittery formation near the contact with the

Rye formation suggest that recrystallization in those areas out­ lasted regional deformation. Causes of Metamorphism

Most progressive metamorphic effects appear to be directly related to the intrusion of granitic or near-granitic igneous masses of the Hillsboro plutonic series. The metamorphic rocks adjacent to the Exeter diorite and the Newburyport quartz diorite of that plutonic series, on the other hand, apparently were not notably affected by the emplacement of those igneous rocks.

The differences in degree of metamorphism may perhaps be explained by (1) the total available heat during the time of intrusion; (2) the susceptibility of the host rocks to meta­ morphism; or (3) the presence or absence of solutions and volatiles which may have acted as catalysts.

Evidence of contact metamorphism is present in some rocks.

The previously mentioned random porphyroblasts of biotite in the metamorphic rocks southeast of the quartz monzonite of Rochester and Barrington, which indicate metamorphism post-dating defor­ mation, may be properly considered of thermal, or contact, meta­ morphic origin, A few thin sections of rocks from the Rye for­ mation show relict grains of andalusite in sillimanite, indicating that some degree of contact metamorphism was established prior to the superposition of regional metamorphism if it be assumed that andalusite forms during Contact metamorphism only. According to

Turner and Verhoogen (1960, p. 470), increased pressure promotes 162 the conversion of andalusite to sillimanite; however, various opinions have been expressed by others regarding the formation of andalusite, sillimanite, and kyanite. (See Fyfe, Turner, and

Verhoogen, 1958, p. 164-165.)

Those parts of the Kittery and Eliot formations included in bodies of the Exeter diorite and those in marginal contact with the diorite are thermally metamorphosed, and exhibit random porphyroblasts of biotite, actinolite, and diopside athwart earlier- developed schistosity.

Evidence of retrograde metamorphism is most comnon in rocks of the Rye formation, where there was observed (1) sericite, epidote-zoisite, albite, and calcite derived in part from plagio-

clase; (2) biotite, epidote-zoisite, magnetite, and chlorite

from amphibole; (3) chlorite, magnetite, and rutile from biotite;

(4) chlorite and biotite from garnet; and (5) muscovite from

sillimanite. The alterations are most pronounced, and pseudo- morphs most common, in those rocks which are granulated and sheared.

According to Turner and Verhoogen (1960, p. 486-487), deformation

or hydrothermal activity following the principal stage of meta­ morphism have been cited as causes of retrograde metamorphism. STRATIGRAPHIC CORRELATIONS

General Statement

One of the major geologic problems of southeastern New

Hampshire and adjacent parts of Massachusetts and Maine is strati­ graphic correlation, inasmuch as there is no known paleontologic, structural, or stratigraphic information from those areas. In lieu of specific data, and because of the large unmapped contiguous areas, several tenuous correlations have been advanced in relating the rocks of southeastern New Hampshire to the fossiliferous rocks of east and east-central Massachusetts, southwestern Maine, and western New Hampshire.

Correlation with Eastern and East-Central Massachusetts

Rocks of the Merrimack group of southern New Hampshire and eastern Massachusetts, which include the Kittery, Eliot, and

Berwick formations of present nomenclature, were originally assigned by Hitchcock (1874, pp. 37, 336) to Early Paleozoic or Late

Precambrlan age. Katz (1917, p. 101), however, correlated the

Kittery and Eliot formations of northeastern Massachusetts and southeastern New Hampshire with the Oakdale quartzite and Worcester phyllite of east-central Massachusetts and, inasmuch as Perry (1885, p. 157) and White (1912, p. 114) reported the fossil Lepidodendron acuminatum from the Worcester "coal" mine north of Worcester,

163 164

Massachusetts, designated the Kittery and Eliot formations

Carboniferous in age. The validity of the fossils has been dis­ puted to this date by most workers in the area.

I n 1962, the writer viewed the specimen of Lepidodendron sp, which is housed in the Asherst College Museum, Amherst,

Massachusetts, and which is reproduced in the frontispiece of

the publication by Perry and Emerson (1903). With the exception

of several poorly glued fractures, it is identifiable as the

specimen depicted. Professor George W. Bain, Department of

Geology, Amherst College (oral communication, 1562), suggested

the possibility that the fossil may in fact be a predecessor of the

Lepidodendron acuminatum and perhaps be of Devonian age. An ad­

ditional similar specimen, found by the writer in the museum of the

Worcester Society of Natural History, Worcester, Massachusetts, in

the summer of 1959, was identified only as having been found in

the Worcester "coal” mine.

Professor Mar land P. Billings, Department of Geology, Harvard

University, Cambridge, Massachusetts (personal communication, 1959),

reported that carbonaceous material from the Worcester "coal" mine

was very much like the meta-anthracite of Carboniferous age from

the mine in Cranston, Rhode Island.

A flaw in the observations of Emerson (1917, p . 77),

however, may be a clue to the disparity of opinions concerning

the ages of the formations involved. He considered that the 165

Oakdale quartzite graded into the Worcester phyllite, in Massa­ chusetts, without any structural discontinuity. The writer, on the other hand, has found evidence in the Clinton, Shirley, and

Shrewsbury quadrangles, Massachusetts (Novotny, 1961), that the

Oakdale quartzite is in fault contact with the Worcester formation and may be separated from it by a considerable span of geologic time. Jahns (1952, p. 102) agrees with the writer, having found pebbles, which he identified as Merrimack quartzite, in the base of the Worcester formation.

Billings (1956, p. 102) indicated that the fossiliferous

Worcester "coal” mine area of Worcester formation may be a down- folded or down-faulted remnant of phyllite younger than the surround­ ing rocks.

Correlation with Southwestern Maine

Correlation of formations of southeastern New Hampshire with those of southwestern Maine began with Perkins and Smith (1925, p. 223), who considered both the Vassalboro and Waterville for­ mations, the latter containing Monograptus colbiensis, to be of

Middle Silurian age. Fisher (1941, p. 137-139, 142) correlated the

Sabbatus formation to the southwest of Waterville, Maine, with the

Waterville and Berwick formations on the basis of lithologic simi­ larity and apparent structural continuity, and hence concluded the age to be Middle Silurian. Fisher's Pejepscot formation (1941, p. 142) 166

Included the equivalents of the Kittery and Berwick formations.

Fisher, however, did not completely trace the stratigraphic units along strike, and a gap of about 10 miles separates his area from that of Katz (1917, p. 165-177).

Billings (1956, p. 104) considered that lithologic similarity and a presumed continuity along the strike of formations would tentatively correlate the Kittery, Eliot, and Berwick formations of southeastern New Hampshire with the Waterville and Vassalboro formations of Middle Silurian age and has so dated them. However, the metamorphic rocks between southeastern New Hampshire and the

Waterville area are perforated by several plutonic igneous masses, which make correlation along strike quite speculative.

Correlation with Western New Hampshire

The Littleton formation, which is considered to be Lower

Devonian on paleontologic evidence (Billings and Cleaves, 1934, p. 412-438), has been traced by means of similar lithology across strike into southeastern New Hampshire from the type locality in western New Hampshire. Both Freedman (1950, p. 488) and the writer have found the Littleton formation to be structurally conformable with the underlying Berwick formation, although the contact of the two units is nowhere exposed. The Berwick, Eliot, and Kittery formations thus are considered to be of Early Devonian age or older. 167

Although the above correlation appears valid, It should be pointed out that the continuity of the mapped Lower Devonian

Littleton formation (Billings, 1955) is interrupted by faults and large plutonlc bodies. It is therefore conceivable that, though the rocks are lithologically similar throughout the area, not all are part of the Littleton formation. In addition, facies changes which may have occurred during deposition could complicate the tracing of the Littleton formation across the strike from the type locality to southeastern New Hampshire.

Evidence from Igneous Rocks

The metamorphic rocks of the Dover-Exeter-Portsmouth region are intruded by igneous rocks of the Upper Devonian(?) Hillsboro plutonlc series and the Mississippian(?) White Mountain plutonic series, which indicates that the stratigraphic units are Upper

Devonian or older in age. As noted in the discussion of the Exeter diorite of the Hillsboro series, however, a lead-alpha date of

307 ±10 rr;.y. for that igneous rock, according to Kulp's revised geologic time scale (1961, p. 1105-1114), would indicate the

Hillsboro series is Pennsylvanian in age. The Kittery, Eliot, and

Berwick formations, which have been intruded by the Exeter diorite, are therefore Pennsylvanian or older. Conclusions

Three reasonable methods for the determination of the age

of metamorphic rocks in the Dover-Exeter-Portsmouth region yield different results. 1) Correlation of the Merrimack group, which

Includes the Kittery, Eliot, and Berwick formations, with fossil-

iferous strata in southwestern Maine indicates a Middle Silurian(?)

age for the Merrimack group. 2) Correlation of the Littleton

formation across New Hampshire indicates that the Littleton

formation in the southeastern part of the state is Lower Devonian,

and that the underlying Berwick, Eliot and Kittery formations are

Lower Devonian or older. 3) A lead-alpha age determination of

plutonlc rocks that intrude the Kittery, Eliot and Berwick forma­

tions indicates a Pennsylvanian or older age for those formations.

The weight of evidence, therefore, suggests a Lower Devonian age

for the Littleton formation and a Middle Silurian(?) age for the

Kittery, Eliot, and Berwick formations. The Rye formation, which

is presumed to lie conformably below the Merrimack group,is there­

fore Middle Silurian(?) or older, perhaps Ordovician(?). SUMMARY OF GEOLOGIC HISTORY

The earliest recorded geologic event in the Dover-Exeter-

Portsmouth area is the deposition of the marine Ordovician(?) Rye formation, approximately 4,000 feet in thickness. The occurrence of many interbeds and lenses of mafic volcanic tuff in the upper of the two members of the formation indicates that extensive volcanism took place during this time.

Deposited on the Ordovician(?) Rye formation, without interruption of sedimentation, was the Silurian(?) Kittery for­ mation. This was followed in sequence, conformably and transition­ ally, by the deposition of the Eliot and Berwick formations. The three Silurian(?) units totalled approximately 19,000 feet in thickness and are considered to be of marine origin. The marine

Lower Devonian Littleton formation appears to have been deposited conformably on the Berwick formation, although data in the area studied are inconclusive.

Although Freedman (1950, p. 489) suggests that the source area of sedimentary material was to the east, there is no evidence in the rocks of the Dover-Exeter-Portsmouth region to substantiate the hypothesis. The writer, however, does agree with the idea that the source terrane was either distant or low-lying, because of the fine-grained character of the original sedimentary materials.

169 170

The rocks deposited from Ordovician to Early Devonian time were involved in tectonic deformation related either to the Middle

Devonian Acadian disturbance or to the Pennsylvanian Appalachian orogeny. During this time the northeast-southwest trending major and minor folds were developed in southeastern New Hampshire, accompanied by the syntectonic to late-tectonic intrusions of the

Hillsboro plutonlc series, which ranged in composition from gabbro to granite and granite pegmatite. During this deformation and igneous activity, the sedimentary and volcanic rocks were metamorphosed, the maximum degree being to the staurolite grade in the northwest and to the sillimanlte grade in the coastal region.

Metamorphism was most pronounced in areas surrounding granitic or monzonitic intrusions. Some minor metamorphic effects, apparently later than the deformation, were also produced locally around some intrusive masses.

Emplaced in part synchronously with, and in part later than, the deformation of the region, were the bodies of the Hillsboro plutonic series. In order of emplacement, they are (1) Breakfast

Hill granite and pegmatite; (2) Newburyport quartz diorite;

(3) porphyritic quartz monzonite; (4) Exeter diorite; and (5) quartz monzonite. 171

Many post-metamorphism camptonite sills and dikes and one dike of granophyre were intruded during post-tectonic activity, as part of the Mississippian(?) White Mountain plutonic-volcanic series.

The final geologic event, with the exception of minor recent alluviation and shoreline modification, was Pleistocene glaci­ ation. The reported presence of only one till suggests but one stage of glaciation. ECONOMIC GEOLOGY

Economic mineral resources of the Dover-Exeter-Portsmouth region consist primarily of sands, gravels, and clays of Pleistocene age, D. H. Chapman (1950, p. 14) reported that on the peninsula

southeast of Dover as many as 20 brickyards were once in existence.

The Eno Brickyard west of Exeter was still operative in 1954,

The lafolla quarries south of Portsmouth on Peverly Hill

are worked for crushed rock from the upper member of the Rye

formation. An abandoned crushed-rock quarry is located approxi­ mately 1.25 miles southwest of New Castle in Portsmouth,

According to local sources, operations there were originally based on the abundant mafic dikes and sills, but the enclosing metamorphic rocks of the upper member of the Rye formation also

proved to be satisfactory for the purpose and were used in the

later years of the operation.

On the eastern slope of Great Hill, Newmarket, is a prospect

pit in a partly silicified portion of the margin of the Exeter

diorite from which silver was reported (Meyers and Stewart, 1956,

p. 29). Inspection by the writer revealed only black fibrous

tourmaline in clear to milky quartz.

The writer observed,in 1952, specimens of galena, sphalerite,

chalcopyrite, and pyrite from an excavation in the Exeter diorite

approximately 1.50 miles east-northeast of Durham. Mineral quantities

were insufficient for exploitation.

172 Several abandoned prospect pits in pegmatites in the area

of quartz monzonite of Rochester and Barrington attest to past mineral exploration. There is no record of mineral production

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Pt. 2, Elements of optical mineralogy, 4th ed.: New York,

John Wiley and Sons, Inc., 551 p. AUTOBIOGRAPHY

I, Robert Frank Novotny, was born in Springfield, Massachusetts,

March 10, 1926* I received my secondary-school education in the public schools of West Springfield, Massachusetts. A year of under­ graduate study was taken at American International College, Spring­ field, Massachusetts in 1943, prior to entrance into the United

States Army Air Force for 17 months' service. Further undergraduate and graduate training was undertaken at Syracuse University, which granted me the Bachelor of Arts degree in 1950 and the Master of

Science degree in 1952. During the last two and one-half years at

Syracuse University I was a departmental assistant in the Department of Geology, teaching elementary geology laboratory courses.

During the 1951-1952 school year I was an instructor in the

Department of Geology and Geography at the University of New

Hampshire.

During the academic years 1952-1954, I was a graduate assistant

in the Department of Geology at The Ohio State University. For the

1954-1955 school year I was awarded the John A. Bownocker Fellowship

in the Department of Geology.

During the academic year 1955-1956, I was an instructor in the

Department of Geology, University of Connecticut.

In September 1956, I commenced duties with the New England Branch

of Regional Geology, United States Geological Survey, Boston,

Massachusetts, where I am presently employed.

182 t a b u : i

APPROXIMATE MODES OF THE RYE FORMATION, LOWER METASEDIMF.NTARY MEiBER F = 1 jl)UC I i.u'n

iiK-ral ■; T 1 ' I ! 1

7 1 u L2 : i i I 1 1 0 1 I 1 i " 1 i r ...... 1 i ] I'orpl.yroblj s l s i 1 Bintite.... 13 9 10 18 i 7 ! * •

! 20 23 * , 1 • , i ! GarneL ,. jr. 13 ! * * , I 3 l 11 im a m te. , ! * 11 • • i • • • 1

’uart.,...... 4 J 27 44 41 ,S 58 ! 3! j 27 ! 30 I 20 48 & 13

Plae.i or 1 ase...... 3 23 22 24 24 ■' 17 10 13 : 8 40 1 28 ! 16 I 41 Microci ine ...... I tr .. 3 3 i , . 6 • V ., i .. ! •• B io tile ...... 22 10 12 L2 y i 8 19 13 1 14 : 9 21 tr 8 I I Chlori te ...... 2 tr tr 4 ! 2 .. 4 * 2 4 ! ,, Muscovite...... 1 tr 14 tr tr ; tr 13 1 : 31 3 I I1 1 S ericite...... tr tr 2 3 , . .. i * • I .. • • ,.

3 i 1LinanLte...... • * 7 1 9 i 14 I •* Hornblende ...... • ., • « ; ,. 8 i 36 Tourmaline...... 1 tr cr tr tr 3 tr j 1 *. Apati te...... tr tr tr tr tr tr tr tr tr tr ! tr tr tr Zircon...... tr tr tr tr tr tr tr tr tr tr tr tr tr Epidote-aiusito ...... tr tr tr tr , tr .. ,, 4 * .. i Spbene...... tr ., • .. ,. 1 2 Magnetite ...... tr tr tr tr tr tr 1 2 1 tr 1

Per cent anorthite in plagtocLase... 32-3/; 1 2o-32 10-13 10-13 1 35 3i-35 ; 11, 31-36 15 35 34-65 59-64 O m o 1 Size oi porphyroblasts .'JO- .30- .30- .43- 1 2.80- .40- 1.30- 1 . 3 0 2.40 2.40 3.60 3.00 .60 1.40 * ’ 3.50

Size oi ground],ass (v„i.)...... 'Ah-\ .OOp- . 0 0 4 - .093-: .005- . 0 6 - ,004- .006- ; .01- .06- .005- .19- .13- i. 30 i .30 . 1 9 .28 1.32 30 .24 .20 1.80 .22 .60 ,t>6 .66

Texture. , ) 1) 3 S .3

...... 1

Mineral sizes are complete range observed

S = Schistose

G = Granoblastic

1. Quartz-plagioclasc-biotitc schist S. Garnetiferous quartz-tnica schist

2. Garnet-biotite-quartz schist 9. Quartz-silliTPinite-bioti te schist

3. Quartz-mica-plagioclase schist 10. Quartz-sillimanite-mica schist

4. Quartz-biotite-garnet-plagioclase schist 11. Quartz-biotite-sillimanite schist

5. Feldspathic quartzite 12. Plagioclase-diopside amphibolite

6. Carnctiferous feldspathic quartzite 13. Plagioclase auphibolite

7. Garnetiferous quartz-biotite schist TABLE 2

APPROXIMATE MODES OF THE RYE FORMATION, UPPER METAVOLCAMIC MEMBER

Specimen Minerals ! i 1 2 3 4 5 6 7 8 9 ;

~t Porphyroblasts Plagioclase...... a • * a • • a a 12 31 29 a a i Hornblende...... a » • a a a .. a a a a 27 a a •*

Groundmass Quartz...... 29 41 12 87 40 38 23 26 tr Plagioclase...... 16 25 13 2 23 7 19 29 35 1 1 a * .. 2 2 a a a a Microcline...... •* Biotite...... 52 • a 75 7 21 16 16 2 1

Chlorite...... tr a a tr 1 1 6 a *

...... ! Muscovite tr * 1 .. • • tr 2 a a « a a • s.- ...... 2 Serlclte • * tr a a tr tr 1 LA

Garnet ...... •••• .. 4 a a 1 a a a * a a

Actinolite...... • a 23 a a a a a a a a

Hornblende ...... a a * • a a a a a a a a * *

Calcite ...... • a 1 a a .. a a a a tr

i Tourmaline ...... tr • . tr a a • • a a a a f * * • • Apatite ...... tr tr tr tr tr tr tr tr tr J Zircon ...... tr tr tr tr tr tr tr a a tr

Epidote-zoisite ...... 1 8 a a a a tr 1 1 2 1

Sphene ...... 1 tr 1 a • a a tr a a 4 2 3

Magnetite...... i tr tr a a 1 1 1 I 2 Pyrite...... ! tr a a tr a a a a a a a a tr

; Per cent anorthite j j in plagioclase...... 32-39 33-47 15-17 13 11-15 13-16 1 14-16 25-49 25-48 1 O r- 1 ! Size of porphyroblasts (am.)... ' a • a a a a a a | .30- • | .30- .30- a a 1 1 a a a a a a 9.10 : 4.20 • • 1 3-9 i 1.14

Size of groundmass (am.)...... 005- .005- .019- .06- .001- .005- i .008-* .019- .005- .158 .152 .133 .12 .19 .04 j .06 .19 .76 i _ | Texture...... SS SG | Gn Gn Gn Jn* S

Mineral sizes are complete tange observed

S =* Schistose

G * Granoblastic

Gn - Gneissic

1. Feldspathic quartz-biotlte schist 5.-6. Quartz-biotlte-plagioclase gneiss

2. Feldspathic quartz-actinolite schist 7. Injection and permeation gneiss

3. Biotite schist 8. Quartz-plagioclase-hornblende schist

4. Quartzite 9. Plagioclase amphibolite TABLE 3 APPROXIMATE MODES OF THE KITTERY FORMATION

S p e c i m e n

i 1 1 1 I 2 3 4 5 6 7 8 9 1 I X -- f f ' | 1 1 Porphyroblasts I A c t i n o l i t e ...... • * ■ • i • * * • « • * * • • 22 .. 1 G r o u n d m a s s Q u a r t z ...... 23 15 52 5 50 79 72 45 52 Plagioclase...... 2 tr • • • * 15 5 12 19 13 M i c r o c l i n e ...... • • • • • • • • • • • 3 B i o t i t e...... • ■ • • 42 47 29 • • • • tr 7 C h L o r i t e ...... ; 2 53 tr 7 • ■ 7 4 3 10 S e r i c i c e...... 6b 28 4 36 5 2 2 3 A c t i n o l i t e ...... * * « • • » • • • • * • # • • 9 C a l c i t e ...... i tr tr • * • * 3 1 • • * • tr * * T o u r m a l i n e ...... • • * * J • • ■ • tr * » Apat i te...... • .. 1 • • tr tr * • tr tr Zi rc o n ...... tr f r i tr tr tr • tr tr lI Epidote-zoisite...... 5 : • • tr • • • • • * • • 3 8 S p h e n e...... •• .. • i • « • • ■ • 1 1 1 P y r i t e ...... tr 2 ! 2 I 4 1 1 tr Limoni te ...... • « • * * ; 3 • • • • • * • • • • Ilneni te ...... •• • • • • tr • • • ■ 8 • s • *

Pur cent anorthite : i 36-47! 5 31-34 31 »n plagioclase...... 7-9 9 » • I 6 ' Si.ze of porphyroblasts (cm,)... * * • • .114- * • • • • • ** •• ; • • 1 ■ . 76 • • * * • • 1 1 Size of groundtzass (mm.)...... 006- .007- .009- , .010- .009-! .008- .009-; .019-! .005- .057 .057 .475 .076 .878 , .19 .019 .095 | .19 i 1 T e x t u r e ...... SS SSS G G i G 1 G _ ------.. i - - ■ L - . ____ 1 . ..1. .. .. ,j_

Mineral sizes are complete range observed

S = Schistose

G = Granoblastic

1.-2. Phyllito

3. Quartz-biotite schist

4. Biotite-sericite schist

5. Feldspathic quartz-biotite schist

6. Quartzite

7. Feldspathic quartzite

8.-9. Lioe-silicate rock TABLE 4

APPROXIMATE MODES OF THE ELIOT FORMATION

Specimen Minerals f 1 2 3 4 5 6 7 8 9 10 11 12

Porphyroblasts a a a a a a a a a Dolomite...... • • • • 12 a a a a a a • a a a a a a a a a a a a Biotite...... • a • a a a 31 a a a a a a a a a a 18 Actinolite...... • a a a a a a a a • a a a a a a

Groundmass Quartz...... 48 10 22 47 60 20 49 60 59 76 52 61 Plagioclase...... 7 4 10 5 13 5 5 a a 15 6 25 15 a a a a 1 a a • a Biotite...... • * • a a a 19 67 tr a a a a 25 a a • a Chlorite...... • » 21 51 3 8 tr Serlcite...... 62 a a 5 a a 3 6 12 7 a « a a a • 8 a a Actinolite...... • a a a a a a a a a a a a a a a a a a a a a a a Dolomite...... • a a a a a a a a a a a 40 a a a a 14 10 tr Calcite ...... a a * a a a a a tr tr a a a a Tourmaline...... a a a a tr tr tr a a a a tr tr a a a a a a a a ...... tr a a tr tr a a a a a a Apatite •* a a a a tr tr a a tr tr tr tr Zircon...... •• •• •• a a ...... a a tr tr a a • a tr 15 6 Epldote-zoisite • » • a tr a a tr a a tr Sphene...... • a a a a a tr a a a a Pyrite...... tr 3 a • a a tr 2 tr a a tr tr a a tr Limonite...... tr ■ a 5 a a a a 3 tr tr tr tr a a a a Rutile...... tr tr • a tr tr a a a a tr tr a a a a tr

Per cent anorthite 8 6 9 15 44-49 35-44 in plagioclase...... 7 8 7-8 9-13 11-14 13

Size of porphyroblasts (mm.)... • e 9 9 .247- .057- a a a a a a • a a a .. a a .25-

• * .95 1.14 a a a a a a « a .. a a .38

Size of groundmass (mm.)...... 019- .09- .018- .019- .008- .019- .017- .009- .016- .018- .038- .036- .19 .38 .133 .038 .19 .095 .380 .114 .380 .080 .285 .133

SSS S S S G GCG Texture...... G G ...... - ...... L...

Mineral sizes are complete range observed

S - Schistose

C * Granoblastic

1. Slate 7. Dolomite quartzite

2. Phyllite 8. Chlorite-sericite quartzite

3. Dolomitic phyllite 9. Feldspathic quartzite

4. Quartz-biotite schist 10. Quartzite

5. Feldspathic quartz-biotite schist 11.-12. Lime-silicate rock

6. Biotite schist TABLE 5 APPROXIMATE MODES OF THE BERWICK AND LITTLETON FORMATIONS

Specimen

Minerals i 1 f----- T ■ " 1 3 4 3 1 6 ! 7 8 9 10 I ! 1 I lI 2 Porphyroblasts i Biotite...... 21 29 3 a a 5 18 a a

Muscovite...... • • a a a a a a a a 22 a a Garnet...... a a a a 12 a a a .. 1 2 Stauroli te...... •• .. a a a a a a a a a a 25 a a Actinolite..,...... • • a • a a a a a a 25 8 23 a a a • Diopside...... • • a a a a a a a a 22 a a a a

Groundless Quartz...... 40 50 31 40 67 45 40 50 35 37

Plagioclase...... • • 11 a a a a 21 10 27 19 a a

Microclinc...... • a 5 » a a a a a a a a a a a a a Biotite...... 9 13 11 a a 8 a a a a a a a • 20

Chlorite ...... • • tr tr 6 1 tr a a a a tr ..

Muscovite ...... a • 3 a a a a a a a a a a a a 30 Serici te ...... 27 8 25 50 a a a a .. 8 a a a a Calc i te...... • • 10 a a a a a a 2 tr tr a a a a Tourmaline...... 2 tr 3 tr tr a a a a tr tr tr

Apatite...... * • • • a a a a tr tr a a tr Zircon...... tr • • a a a a tr tr tr tr tr tr

Epidote ...... • a a a a a tr 3 a a 1 a a

Sphene ...... • a a a a a a a tr 1 2 a a

Magnetite...... a • • a a a a a a a tr a a a a tr 1 Pyri te...... I tr 1 1 tr tr tr a a tr

Limoni te...... • * * • a a a a a * a a tr a a a a a a

Per cent anorthite

in plagioclase ...... a • a a a a 1 4 - 1 6 ! 35-40 30-37 25-27 a a a a

Size cf porphyroblasts (inn.)... . 2 0 - a .380- . 1 9 - a a . 2 8 - . 1 9 - j .41- .76- 1.14-

.48 * * .665 .38 a a 2.85 4.18 .75 3.42 1.32 o 1 Size of groundmass (ran.)...... 019- a 0 1 6 - .015- .019- . 0 1 8 - a .016- i.095- .283- .25- ; .170 ,228 . 0 1 8 .057 | .855 . 3 0 .07 .285 .413 ; .33 1 1 i 1 Texture...... S s 1 s ! G C G S s 3 1 G | 1 L. ____ ! 1 1 .J------1

Mineral sizes are complete range observed

S = Schistose

C = Granoblastic

Berwick Formation Littleton Formation

1. Quartz-biotite-sericite schist 9. Quartz-staurolite-mica schist

2. Feldspathic quartz-biotite schist 10. Quartz-gamet-mica schist 3. Biotite-quartz-sericite schist

4. Quartz-sericite schist

5. Feldspathic quartzite 00 1 a Lime-silicate rock TABLE 6

APPROXIMATE MODES OF THE HILLSBORO PLUTONIC SERIES

Minerals

2 3 10 11 12 13 14 15

Plienocrysts Microcline. 42 24

Groundmass Quartz...... 17 24 8 20 21 19 23 30 6 1 le 12 21 23 Plagioclase ...... 19 17 35 43 40 60 55 19 20 42 31 46 14 43 Microc i ine ...... 45 56 38 ; l:> t • 48 • • 56 25 Biotite ...... 1 ; 13 13 17 10 tr I 7 1 Chlorite,,.,,,,.,,,,., # t 1 3 tr 2 tr 2 6 11 tr Muscovite...... 12 ,, b , 12 tr Sericite...... 5 tr 9 10 I 4 L 2 tr Hypersthene...... # , 11 .. j Augite ...... t 54 Hornblende, ...... t 20 50 Garnet...... 1 Tourmaline...... Calc it e...... ,, tr I i Apatite...... ,, tr tr tr tr tr tr Zircon, ...... ,, tr t tr tr tr tr tr cr I Kpidote-zoisi te ...... 2 tr tr 1 2 tr tr tr ; Sphenc...... , * , , # i Magnetite ...... 1 1 I ? ;; - Pyrite...... , ,, ,

Per cent anorthite in plagioclase ...... j-|(; 7-LJ 4 -k '6 }(,->■ 33-43 30-32 30-36; 6-1? j 7-12

3i 2e o[ phenocrysrs (mr.i.)...... It 27 '

j : groundmass Size (:.ri.)...... • . . o' I . i.u- . 1 p. .Of,- .12- ,ff- .12- j 1.60-1 .06- 1 2. 7. i. ')•> ! 1,4'i 4 . . ? ( i 1. j: 2.-2 5.10 14.401 1.HO

T e x t u r e , : , c-': r lV o r i ,1‘ t 1 P i J

Mineral sizes arc complete range observed

C-G = Coarse grained, gneissic

? = Pegmatitic

11 = Hypidiomorphic

Por = Porphyritic

A = Aplitic

Breakfast Hill granite and pegmatite Porphyritic quartz monzonite

1.-3. Granite 12.-13, Porphyritic quartz monzonite

4.-5. Pegmatite 14. Pegmatite

L ). An 1ite Newburyport quartz diorite

6.-8. Quartz dioriLe

9. Pegmatite

10.-11. Diorite autoliclis TABLE 7

APPROXIMATE MODES OF THE HILLSBORO PLUTONIC SERIES f „ .. . Specimen 1 M i n e r a l s •-- 10 u 12 13 14 1 2 3 4 5 6 7 8 9

1 2 12 33 25 28 Quartz...... y 1 1 6 4 22 13 23 IS 56 52 18 Jo Plagioclase...... 23 13 61 57 59 43 20 33 71 30 Oftl a a a 12 17 47 Microcline...... 2 a a 21 62 39 a a a a a a a a a a a a a 8 6 a a a a a a • a Hypersthene...... a a a a a a a a a a a a a 5 a a Augite...... 59 59 21 14 • a a a a a a a « a a a a a a a a a a a Hornblende...... a * a • a a • a 25 a a • a a a a a a a • a a a 4 a a Urallte...... 11 8 a a tr a a 6 8 10 1 3 a a 15 4 Biotite...... 5 6 3 1 tr 2 tr 7 5 8 1 a a Chlorite...... 6 5 1 2 a a a • tr tr aa a a tr a a Muscovite...... tr Sericite...... 1 tr 1 2 4 2 1 6 6 3 a a a a 1 1 a a a a a a Calclte.,...... tr tr a a a a 1 a a tr a a tr a a tr Zircon...... tr tr tr • a a a a tr 1 a a a a 1 tr tr a Apatite...... tr tr tr tr a a a a 2 a a a a a a a a a a a a Garnet...... a * a a a a tr tr 1 3 a a tr a a Epldote-zoislte...... 2 tr 1 tr a a a a a a a a a a 1 tr Sphene...... tr tr tr tr a a 4 tr 2 1 tr tr Magnetite...... 1 2 5 4 tr tr a a tr

Per cent anorthite 11-13 9-15 23 in plagioclase... 41-46 50-54 25-38 33-45 28-38 29-37 4-15 24 43-51 28-33 31 .30- .60- Grain size (mm.)... .36- 1.20- .18- .12- .42- .12- .30- .24- .60- .18- .12- .12- 4.80 4.20 3.30 5.70 6.00 5.58 6.18 1.92 4.32 .90 4,20 .90 1,80 3.60 H Texture...... H H H H 11 H H A rf 11 H A H L. ------Mineral sizes are complete range observed

H ■ Hypidiomorphic

A = Aplitic

Exeter diorite pluton Exeter diorite bosses

1.-2. Gabbro 9. Gabbro

3.-5. Diorite 10. Diorite

6. Quartz monzonite 11. Quartz i

7. Granite 12. Aplite

8, Aplite Quartz monzonite

13.-14. Quartz monzonite TABLE 8

APPROXIMATE MODES OP THE WHITE MOUNTAIN PLUTONIC-VOLCANIC SERIES

^pecicen

Minerals

Phenocrysts Chlori te . .. 4 Labrador ite...... 1 Ti tanaug ite...... 3

Groundr.ias s

Quar tz...... • • * • • » 40 t Plagioclase...... j 5 41 4 / * »

Microcline...... •, * • • * 32

Titanaugite...... 19 8 9 * e

Barkevikite...... * • 30 17 * » 3iotite...... tr tr 4 • • Chlorite...... 14 3 7 ■ • Sericite...... 1 1 2 • • Calcite...... 4 2 1 1

Talc...... tr • * tr • ■ Apatite...... tr tr 1 tr

Ep idote-zois ite...... 1 • * • e 3

Sphene...... • • • • • • 2

Ilnenite...... • * • ■ • • 1

Magnetite...... 6 7 : 6 a »

Pyrite...... * • * * « * 1

Per cent anorthite

in plagioclase...... 5 2-67 5 7-64' 5 7-59 • •

1

Size of phenocrysts (cm.)... • e .31- .48- • e

• • 2.28 2.09 • *

Size of groundmass (err..).... .038-i .133- .05 7-j .010 j .342 .228 .300 | .300 i Texture...... S-P S-P j M S I i , ___L J Mineral sizes are complete range observed

S “ Subophitic 1.-3. Camptonite

S-P ■ Subophitic-porphyritic 4. Granophyre

M “ Micrographic t o

ft

%

29

Quartz o

(Medium- to coarse-gi to buff quartz m o m of ollgoclaie, mlci microperthite, and

Exater

(Light-gray to black, massive diorlte, qt and quartz monzonlt ollgoclase, andetir hyperstbene or augl and mlcrocllne.) 0 Porphyritic qui i (Medium- to coarse-gri 0 k medium-gray, modern 0 A M quartz monzonite, ci microcline phenpcry blotite, and chtori

Newburyport q<

(Medium- to coarse-gr medium-gray quartz ■ oligoclase or andes biotite, and chlori

Breakfast Hill gra

(Medium- to coarse-gr massive to well-fol pegmatite, composed oligoclase, and mus garnet, tourmaline,

METAMORPi

Littleton

(Medium- to coarse-gri bedded, silvery gra] schist, quartz-staui with porphyroblaati Lower Devonian Hillsboro Plutonic Serie (Medium- to coarse-grained, well-foliated, thin- thin- well-foliated, coarse-grained, to (Medium- (Medium* to coarse-grained, porphyritic, porphyritic, coarse-grained, to (Medium* (Medium* to coarse-grained, well-foliated, well-foliated, coarse-grained, to (Medium* Mdu- ocas-rie, ht t tan, to white coarse-grained, to (Medium- ih opyolss f tuoie n garnet,) and staurolite of porphyroblasts with bedded, silvery gray, quartz-staurolite-mlca quartz-staurolite-mlca gray, silvery bedded, schist, quartz-staurollte-garnet-mlca schist, schist, quartz-staurollte-garnet-mlca schist, medium-gray, moderately* to well-foliated well-foliated to moderately* medium-gray, microcline phenocry9ta and hornblende, chlorite,) and hornblende, and blotite, phenocry9ta microcline medium-gray quartz diorite, composed of of composed diorite, quartz medium-gray of chiefly composed monzonite, quartz massive to well-foliated granite and and granite well-foliated to massive chlorite.) hornblende, and quartz, biotite, andesine, or oligoclase garnet, tourmaline, and blotite,) and tourmaline, garnet, oligoclase, and muscovite, with minor minor with muscovite, and microcline, quartz, of oligoclase, composed pegmatite, rafs Hl gaie n pegmatite and granite Hill Breakfast Porphyritic quartz monzonite quartz Porphyritic ebrpr qat diorite quartz Nevburyport iteo formation Littleton METAMORPHIC ROCKS METAMORPHIC nqd bh« qm p ^ dotted where concealed; alternating dots and dots alternating concealed; where dotted ^ ahswee bcrdb h xtr diorite 0 Exeter the by pluton, obscured where dashes 4 2 0 2 Z *'•'* 0 111 0 Z < Z tieo etcl cleavage vertical of Strike > t f e - hwn taeo xa paeaddrcino plunge of direction and plane axial of trace Showing or cealed; queried where doubtful, where queried cealed; of axis, Dashed where approximately located; approximately where Dashed axis, of hr dse hr Ifre; otdwee con­ where dotted Inferred; where dashed short xs Dse hr prxmtl locatea, approximately where Dashed axis. Strike and dip of vertical beds vertical of dip and Strike tie fvria foliation vertical of Strike foliation of dip and Strike tie n i o cleavage of dip and Strike Strike and dip of beds of dip and Strike Overturned sync sync line Overturned ------•>' 170 55 50 >

r

EXPLANATION

IGNEOUS ROCKS SYMBOLS

\ qin .. Contact Quartz monzonite Dashed where approxlnately located; short dashed (Medium* to coarse-grained, massive, light-gray where Inferred; dotted where concealed, to buff quartz monzonite, composed chiefly of oligoclase, microcline, microcline- nicroperthite, and quartz,)

D Fault

78\ 1 1 where approximately located; short dashed where Inferred; queried diere doubtful, U, Exeter diorite u p t h r o w side; D, d o w n t h r o w aide,

(Light-gray to black, fine- to coarse-grained, massive diorite, quartz diorite, gabbro, and quartz monzonite, composed chiefly of H H ■■> 11)1 Mi Ml h oligoclase, andesine, or labradorite, hypersthene or augite, hornblende, blotite, Overturned anticline and microcline,) H

V*« 'V

5 rityin ry- (Hedtnm- to co«rse-griinedl whit miiilve to well-foliated grani pegmatite, composed of quartz, oligoclase, and muscovite, wit garnet, tourmaline, m d biotit

METAMORPHIC ROCKS

Littleton formation

(Medium- to coarse-grained, veil bedded, silvery gray, quartz-si schist, quartz-staurolite-gamt with porphyroblasts of staurol:

Berwick tomation

(Fine- to medium-grained, thln-bi massive, light* to dark-gray oi feldspathic quartz-blotite sch: quartz-serlcite schist, and qui schist; fine- to medium-gralne< to light gray-green, thin to tl lenses of lime-silicate rock, i oligoclase-andesine, actinoliti garnet, epidote-zoisite, calcil minor beds oi i ;ldspathic quarl Eliot formation

(Dark-gray slate; dark-gray to da phylllte, commonly doloraitlc; 1 gray to black blotite schist, q schist, and feldspathic quartz- schist; massive, light-gray to green, fine-grained quartzite, feldspathic, in part dolomltic; green to brown, fine- to medium silicate rock, containing actln

Kittery formation

(Dark-gray slate; dark gray-green phyllite; fine- to medium-grain laminated to massive, poorly- t foliated quartz-biotite schist, sericlte schist, and feldspathl biotlte schist, commonly calcar actinolitic; light gray-green t well-bedded to massive, fine-gr and feldspathic quartzite; thin massive, medium-grained, light- light gray-green lime-silicate

Orv Oim

Rye formation t (Upper metavolcanic member: Orv medium- to coarse-grained, foli biotite-plagiodase gneiss; fin fine-grained, maroon feldspathl blotite schist and fine-grained feldspathic quartz-actinollte s to coarse-grained, dark-gray bi hornblendlc injection and perme dark-green to black, fine- to c amphibollte and hornblende schl fine-grained gray quartzite. Lower metasedimentary member: 0 coarse-grained, light- to dark- mica schist and quartzo-feldspa commonly containing garnet and fine- to medium-grained, thin-b massive, gray quartzite, common o ; t v 4 v phyllitc, commonly dolomitic; to dark* tr gray to black blotite schist, quartz-biotite 3 schist, and feldspathic quartz-biotite j * schist; massive, ligbt-gray to light gray- w green, fine-grained quartzite, in part Abandoned quarry feldspathic, in part dolomitic; light gray- green to brown, fine- to medium-grained, lime- silicate rock, containing actinolite.)

Isograds

Hachures point toward rocks of higher metamorphlc grade. Kittery formation

(Dark-gray slate; dark gray-green to silvery gray phylllte; fine- to medium-grained, finely- laminated to massive, poorly- to well- foliated quartz-biotite schist, biotlte- sericite schist, and feldspathic quartz- biotite schist, commonly calcareous and actinolitic; light gray-green to dark-gray, well-bedded to massive, fine-grained quartzite and feldspathic quartzite; thin-bedded to massive, medium-grained, light-gray to light gray-green lime-silicate rock,) J

O rv O rm

Rye formation

(Upper inetavolcanic member: Orv - dark-gray, medium- to coarse-grained, foliated quartz- biotite-plagioclase gneiss; finely Interlaminated z fine-grained, maroon feldspathic quartz- < biotite schist and fine-grained gray-green feldspathic quartz-actlnollte schist; medium* to coarse-grained, dark-gray biotltlc or hornblendlc injection and permeation gneiss; >>0 0 dark-green to black, fine- to coarse-grained K amphlbollte and hornblende schist; minor 0 fine-grained gray quartzite, lower metasedlmentary member: Orm - fine- to coarse-grained, light- to dark-gray and black mica schist and quartzo-feldspathic schist, commonly containing garnet and sillimanite; fine- to medium-grained, thin-bedded to massive, gray quartzite, camonly fa1/Un*PMf inil ------1f.--..■ a . , hlHltU (Medium* to cotrse-grained, white to tan, 'Strike and dip of foliation XT massive to well-foliated granite and I : K M t r i m t i r * pegmatite, compoied of quartz, microcline,

i> Whiti tM d U tk l h» Ji oligoclase, and muscovite, with minor garnet, tourmaline, and blotite,) J A t

Strike of vertical foliation

dtornit METAMORPHIC ROCKS 5 0 bint A

A Strike and dip of cleavage C 0 Z c < 0 > # Littleton formation Z Oi 0 W (Medium* to coarse-grained, well-foliated, thin- > Strike of vertical cleavage 0 III ? bedded, silvery gray, quartz*staurolite*mlca 0 schist, quartz-stauroltte-garnet-mlca schist, Q J with porphyroblasts of staurollte and garnet.) J * 1 5 \ Bearing and plunge of Uneatlon

Kay be combined with planar features, Letter symbols indicate nature of Uneatlon; FA, small Berwick formation fold axes; M, mineral alignment; C, crinkles or corrugations; CB, cleavage-bedding Intersection, (fine* to medium-grained, thin-bedded to massive, light- to dark-gray or black feldspathic quartz-biotite schist, biotite- 77 quartz-serlcite schist, and quartz-serlcite schist; fine- to medium-grained, light-gray to light gray-green, thin to thick beds and Strike and dip of Joint lenses of lime-silicate rock, containing oligoclase-andesine, actinollte, diopslde, garnet, epidote-zoisite, calcite, and biotite; minor beds of feldspathic quartzite,) AT Strike of vertical joint

K Eliot formation o- Z Operating quarry awl* aw A*t • I /tf a > A nrLf_n*nir S*A < w e & n a t f ) ' r A . .. . J

Littli Sogoinori Atlantic

13

SECTION ALONG LINE A-A

I

Seo Level

SECTION ALONG LINE B-B' SECTION ALONG LINE C-C'

"" ' — — P. II I"'"'" I" ■ " ■—IN— ■ ■! — I , — ■ ■■■ -- - Topogroptiic bast by a U. S. Geological Survey GEOLOGIC MAP AND SECTIONS OF T NEW I

I

*lJfd * m w conmonly containing; diops , ..

A/B Oceon ^

- S i o L e v e l

A-A

SCALE 1 62SOC

5(0 Level aMUHHH CONTOUR INTERVAL 2 «ruM fS Mf»N SU [

SECTION ALONG LINE C-C'

MAP AND SECTIONS OF THE DOVER-EXETER-PORTSMOUTH i NEW HAMPSHIRE 1963 i c n w , ana leiaipicnic qua schist; massive, lighter ay green, fine-grained quarttl feldspathic, In part dolonl green to brown, fine- to ne illlcate rock, containing a

Kittery formatlo

(Dark-gray slate; dark gray-g phylllte; fine- to medlun-g laminated to massive, poorl foliated quartz-biotite sch sericlte schist, and feldsp blotite schist, conmonly ca sctlnolitic; light gray-gre well-bedded to massive, fin and feldspathic quartzite; massive, medium-grained, 11 light gray-green lime-sillc

Rye formation

(Upper metavolcanlc member: medium- to coarse-grained, biotite-plaglodase gnelas; fine-grained, maroon feldsp biotite schist and iine-gra feldspathic quartz-actlnoll to coarse-grained, dark-gra hornblendic injection and p dark-green to black, fine- amphibollte and hornblende fine-grained gray quartzite Lower metasedlmentary member coarse-grained, light- to d mica schist and quartzo-fel conmonly containing garnet fine- to medium-grained, th massive, gray quartzite, co feldspathic and garnet Ifere coarse-erained. dark-ereen feldspathic and garnet iferous; fine- to coarse-grained, dark-green to black amphibolite, caimonly containing dlopside and garnet,)

APPROmiUlf MIAS CECUMN0N1%6

SCAIF. 1 62 500 1 MiJS Ei rr i.-l woe imc IT 4.: t i } i

GTHU H H -E ^ CONTrjIjP iNrffiftl 20 FFt'F ' MijM i'i MiAhi CjfA iMl

Geology by R,F, Novotny, 1953-1954

R-EXETER-PORTSMOUTH REGION RE griy 10 duck oioiue scnui, quanz-oioiiie j ichlit, and feldspathic quartz-biotite J V * schist; 4 light-gray to light gray- W green, fine-grained quartzite, in part Abandoned quarry feldspathic, in part dolomltic; light gray- green to brown, fine- to medium-grained, lime- silicate rock, containing actinolite,)

lsogradi

Hichures point toward rocks of hlghar Mtaorphlc grade, Kittery formation

(Dark-gray slate; dark gray-green to silvery gray phylllte; fine- to medium-grained, finely- laminated to massive, poorly* to uell- foliated quartz-biotite schist, biotlte- sericite schist, and feldspathic quartz- biotite schist, commonly calcareous and actinolitic; light gray-green to dark-gray, veil-bedded to massive, fine-grained quartzite and feldspathic quartzite; thin-bedded to massive, medium-grained, light-gray to light gray-green lime-slllcate rock,) J

O r v Orm

Rye formation

(Upper metavolcanic member: Orv— dark-gray, medium- to coarse-grained, foliated quartz- biotlte-plagloclase gneiss; finely interlaminated fine-grained, maroon feldspathic quartz- z < biotite schist and fine-grained gray-green feldspathic quartz-actinolite schist; medium- 5 to coarse-grained, dark-gray biotitic or hornblendic injection and permeation gneiss; % o dark-green to black, fine- to coarse-grained IT amphibollte and hornblende schist; minor 0 fine-grained gray quartzite, Lower metasedimentary member: Orm fine- to coarse-grained, light- to dark-gray and black mica schist and quartzo-feldspathic schist, commonly containing garnet and sillimanite; fine- to medium-grained, thin-bedded to