Configuration of the Bedrock Surface of the District of Columbia and Vicinity

GEOLOGICAL SURVEY PROFESSIONAL PAPER 217

By N. H. DARTON

GEOLOGICAL SURVEY PROFESSIONAL PAPER 217

This report embodies subsurface data of ititerest to engineers and builders compiled from 18go to 1940

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1950 UNITED STATES DEPARTMENT OF THE INTERIOR Oscar L. Chapman, Secretary

GEOLOGICAL SURVEY W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price $1.25 (paper cover) CONTENTS

Preface District of Columbia — Continued Abstrac Northwest Washington — Continued Introdu rtion. Lydecker Tunnel- ______18 Sources of information. Piney Branch relief sewer-____------______- 19 20 Altitude datums. Calvin Coolidge High School ______Southwest Washington-______---______-__ 20 General geologic relations.______General geologic setting. ______20 Bedrock ______Railroad Bridge-_---__------__------20 Sedimentary formations.______Highway Bridge. ______21 Potomac group.______Washington Monument ______21 Upper Cretaceous and Tertiary formations___ Lincoln Memorial_-______-_--_-----____--__ 23 Upland gravels.______Reflecting Pool ______._ ____ 23 Terrace deposits.______Water Gate ______23 Alluvium and artificial fill______Arlington Memorial Bridge ______25 Bedrock contacts ______Jefferson Memorial __ _ __--_-__----__----___ 25 General relations______Agriculture Department B uilding ______27 Tenley to wn Ridge ______Federal building site between llth and 14th Brightwood to Silver Spring______Streets, C and D Streets..-. ______27 Takoma Park to Paint Branch,______Northeast Washington. ______27 Lower part of Washington.______General geologic setting. ______27 Rock decay ______1st Street just north of M Street ______-_---_ 27 Deformation ______7th Street between A and B Streets. -_-.-_____ 27 District of Columbia.______15th and E Streets. ______27 Northwest Washington______Washington Terminal Co ______---____-____ 28 General geologic setting.______Langdon. _ -______-___-__------_---___-_---- 28 Apex Building.______Woodridge ______.__-____. ______28 National Archives Building ______Southeast Washington______28 Internal Revenue Bureau Building______General geologic setting. ______28 Old Post Office Building______9 Naval Gun Factory. ___.-_-__--__--_____-___ 28 Post Office Department Building-______9 St. Elizabeths Hospital-.. -______28 Labor Department and Interstate Commerce Maryland ______29 Commission Buildings--______-____- 9 Prince Georges County. ___------_---__--__-_- 29 Commerce Department Building ______10 Chillum gas tanks___---_-______29 American National Red Cross Buildings__-____ 10 Hyattsville- _ -______29 Interior Department Building-______10 University of Maryland. ______29 17th Street between Pennsylvania Avenue and Agricultural Research Center, Beltsville______30 H Street.______-______----_-- 10 Glenn Dale-.--.-- — _____ — _ — — _„__— 30 19th and 20th Streets, Constitution Avenue and Meadows. _------_------_----_ 30 C Street______..______12 Forestville ______----- ______30 20th and 21st Streets, C and D Streets. ______12 Fort Washington.. ______——— ___ ——— 30 Federal Reserve Board Building.______13 Charles County- — ______31 National Academy of Sciences ______13 Indian Head-______----_-_---_--_-_-_- 31 Navy Department Building______14 Virgi nia -_____-_____-_--__--_--_--_------_---_- 31 State Department Building______15 Arlington County ______31 1st Street near R Street and Florida Avenue. __ 15 Pentagon Building-______-_-__-___- 31 4th Street and Pennsylvania Avenue-______15 Alexandria. ______._.__---_.__--_.- 33 Judiciary Square-______15 Alexandria Tunnel (proposed 1941) ---_____-__ 33 6th and 7th Streets, O Street between___-_-_-_ 17 Fairfax County__--_--_--__--_---__--~----_---_- 33 10th Street between D and E Streets—______17 Seminary Ridge —— ______-__-__---______--- 33 llth and E Streets______-____-_--_-_-_ 17 Fort Hunt. ______------______34 llth and G Streets.______17 Fort Belvoir__--______------_---___ T _ __ 34 14th and R Streets..______-____-__---- 17 Mount Vernon_-__--___------_----_-_---_- 34 14th Street near Irving Street-______17 Data on boreholes and excavations, indicating altitude of Mayflower Hotel and vicinity ______17 bedrock. ______-__----____---_- 34 Soldiers' Home-----____-___--_----___------18 41 in IV CONTENTS ILLUSTRATIONS

Page PLATE 1. Map showing configuration of bedrock surface in the District of Columbia region______!______In pocket 2. Map showing depth to bedrock in part of Washington, D. C______In pocket 3. A, Gravel of Potomac group on gneiss, Harvard Street, east of entrance to Zoological Park; B, Plateau gravel on Calvert formation, Tunlaw Road______-__-_____-______6 4. Terrace deposit of Capitol Hill, south of the Capitol__--_____--_--______-__-____--__------_------6 5. A, Terrace gravel and loam on gneiss, N Street near Twenty-fourth Street NW.; B, Terrace deposit capping arkose in cut on east side of Sixteenth Street at Meridian Hill Park._____ .______--____---_-______6 6. A, Fault on eastern edge of Zoological Park, on Adams Mill Road; B, Fault in rear of Calvert Street near Zc ological Park______7 7. Map and sections of part of "Triangle" area between Seventh and Fifteenth Streets, Constitution Avenue and Pennsylvania A venue. ______In pocket 8. Map and sections of area between Constitution Avenue and D Street, Eighteenth and Twenty-third Streets.__ In pocket FIGURE 1. Diagram showing different datum planes used in the Washington area______-___--__-___--_----_ 2 2. Geologic section across the District of Columbia area, showing the succession and general relations of the principal sedimentary formations______3 3. Sections across the Coastal Plain-Piedmont overlap in Maryland, District of Columbia, and Virginia, showing relations of bedrock floor______4 4. Sections through Washington, showing relations of bedrock and overlying formations______5 5. Section along Wisconsin Avenue from Teneleytown to Potomac River______-___-_-----_--_----- 6 6. Section across fault at Eighteenth and California Streets____-______-_---_------_------7 7. Map and section showing configuration of bedrock surface and boreholes on the site of buildings of the American National Red Cross, between C and E, Seventeenth and Eighteenth Streets NW. ______11 8. Boreholes and configuration of bedrock surface on east side of Seventeenth Street between Pennsylvania Avenue and H Street NW______.___._.___.___._.______.______12 9. Map of area south of Constitution Avenue and west of Fourteenth Street SW______-____-_-____------_--_-- 13 . 10. Sections through boreholes at site of Munitions Building and Navy Department Building, south of Constitution Avenue______14 11. Sections at northeast corner of Navy Department Building.. ______-______-_-__------14 12. Map and sections at site of State Department Building between Twenty-first and Twenty-third, C and D Streets NW______.._____.___.___.__.._.._ —_....— 16 13. Section along Seventeenth Street from Constitution Avenue to DeSales Street______-__-_--_---- 18 14. Section along Lydecker Tunnel from the vicinity of Foundry Branch east to McMillan Reservoir______-____ 19 15. Section along Piney Branch relief sewer, northeast along. Arkansas Avenue and east along Ingraham Street, NW_ _ 20. 16. Map showing configuration of bedrock at Calvin Coolidge High School, Fifth and Tuckerman Streets NW—___ 20 17. Section across Potomac River at railroad bridge-______-__----____-____-_------_------_---_--- — - 21 18. Section across Potomac River at Highway bridge-__-__--__-----__------21 19. Map and sections near Washington Monument_-__-___--__-_---_------_----_------_*-----_--__- 22 20. Map showing configuration of bedrock surface at Lincoln Memorial-______-____----__------__------23 21. Sections under Reflecting Pool, east of Lincoln Memorial, showing position of bedrock surface-—______24 22. Map showing configuration of bedrock surface around Lincoln Memorial and Water Gate. — ______24 23. Section from Potomac River at Water Gate through Lincoln Memorial, Reflecting Pool, and Washington Monument______-_-____---______--____-___-___--__-_---_------_--_---_--- 25 24. Plan and section across Potomac River at Arlington Memorial Bridge, showing probable configuration of bedrock surface as revealed by boreholes at abutments and piers-___---__------_-_----_------_----_---_- 25 25. Boreholes at site of Federal buildings between Eleventh and Fourteeenth, C and D Streets SW—____ — ______26 26. Map of eastern part of Arlington County, Va., showing boreholes in site of Pentagon Building and adjacert area__ 32 27. Sections from southern Fairfax County, Va., eastward into Maryland______-___-______--__------_ 34 PREFACE

By AUCE S. ALLEN

The preparation of this report is the work of a geologist, and the subject of the paper—the position of the contact between the crystalline rocks and the sedimentary formations of the Coastal Plain deposits—is essentially one of interest to geologists. However, much of the source material was contributed by engineers, and it is believed that engineers may constitute the majority of readers of the published volume because of their interest in subsurface condi tions arising from the volume of present-day construction in the Washington area. Therefore a brief account of the background of the investigations that culminated in the preparation of this report may be of interest. Although the report is only now appearing in print, the manuscript was completed by the author in 1940. Publication of scientific reports was inter rupted during the war years and in the interval that followed many buildings in Washington, as well as Government agencies, changed names. Because much of the subsurface data used in the manuscript consists of foundation explorations for buildings, there are many references to names and locations of buildings. The editors have tried to harmonize the references to such names with present usage. None of the additional subsurface information that has become available since the author completed his manuscript, however, has been added. The Geological Survey is continuing to accumulate records of sub surface data and will welcome contribution of boring records for use in future investigations. The span of time during which the author accumulated the data for this paper approximates half a century, paralleling his unusually long term of service on the Geological Survey. Mr. Darton came to Washington in 1886 to start his geological career on the Survey. The association continued until and even beyond his retirement in 1936 except for a 3-year period of work with the Bureau of Mines. His formal retirement caused little change in his professional interests, and he continued to study local geology and to write papers until his death in 1948. Viewing the author's career in its entirety, for his record was unique among geologists for breadth of geologic interest and amount of geologic and topographic mapping throughout the United States, the geologic work in the Washington area forms a small part of his total accomplishments. His bibliography, however, shows that his interest in local geology was a continuing one. His field notebooks show that, at least as early as 1889, he was mapping geologic formations of the Coastal Plain in and around Washington. In 1891 Darton and others prepared a guidebook to the geology of Washington and vicinity for the International Geological Congress meeting. The U. S. Geo logical Survey Atlas folio on the Washington area, which was published in 1901, was the work of Darton and of Arthur Keith who collaborated in the mapping of the crystalline rocks. Although most of Darton's subsequent field assign ments were in the western and southwestern parts of the country, his home remained in Washington. Apparently he collected, from time to time, records VI PREFACE of borings and wells, and made notes on observations of subsurface units tem porarily exposed during excavation for buildings, and other structures. One of his latest publications is a geologic map of "Sedimentary formations of Washington, District of Columbia, and vicinity," which is a revision of the old Washington folio map, using a modern topographic map as a base. The preparation of the manuscript for Professional Paper 217 might be considered a byproduct of the author's geologic mapping activities in the Wash ington area. Its peculiar value lies in the continuity of record over a period of nearly half a century, and in the fact that the geologic interpretations of the subsurface data were made by a geologist thoroughly familiar with local forma tions and their relation to the Coastal Plain geologic province. CONFIGURATION OF THE BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA AND VICINITY

By N. H. DARTON

ABSTRACT they have afforded a basis for the construction of maps A bedrock floor of granite, gneiss, schist, and other crystalline showing configuration and depth. (See pis. 1 and 2,) rocks underlies the District of Columbia region. It is at or Plate 1, which shows the configuration by 50-foot near the surface in the vestern part and descends gradually contour lines, is similar to a map of the region published eastward below the wedge-s:mped mass of overlying sedimentary formations of the Coastal Plain. Much of Washington is built in 1901,1 but modified by later data. Most of the mate across this overlap of unconsolidated material on crystalline rial used in this report is listed in the tables on p",ges rock. In the valley of Rock Creek and in the rolling lands to 35-39. the west the crystalline rocks crop out, but east of Rock Creek Knowledge of the configuration of the bedrock sur the bedrock surface slopes steadily southeastward, and in the face in the Washington area is of great practical impor eastern part of the city it lies several hundred feet below the surface. The position of the bedrock is a matter of great tance in connection with foundations for heavy build interest in planning foundations for governmental and other ings, especially in the western part of the city; in its large buildings, and the relations of the basal gravels of the relation to local water supply throughout the area; and Coastal Plain sediments are important because they contain in its bearing on the structural geology and geologic water supplies, which have been utilized commercially for con history of the region. densing and other purposes. Data as to bedrock configuration are difficult to obtain because SOURCES OF INFORMATION in drilling wells and sinking boreholes the materials are not always identified accurately. At the outcrop, and to some extent The collection of data for this report has been in underground, much of the bedrock is decayed to a micaceous sand that is not everywhere easy to distinguish from sedimen progress for many years, and some of the earlier data tary material. Data from nearby holes help in verification have already been published.2 from one to the other. The bedrock surface, described in this Many detailed plats of test boreholes, with records report and shown on the maps and sections, is the geologic con and other data, were obtained from the office of the tact between the bedrock formations and overlying uncon supervising Architect of the Treasury, Procurement solidated materials of younger sedimentary formations. This surface rarely coincides with the top of hard rock due to the Division; the office of Public Buildings and Grounds; weathering of the bedrock formations to irregular depths. the Corps of Engineers, United States Army; and the Although the southeasterly slope of the bedrock is in general engineering departments of the District of Columbia.8 very regular at a rate of 100-150 feet to the mile, there are Included are the sites of the Washington Monument, local variations in direction and amount. Where data are closely spaced they reveal low mounds and ridges and shallow Jefferson Memorial, Lincoln Memorial, Arlington Me valleys which had been developed as surface features on the morial Bridge, the buildings of the Post Offlbe Depart old pre-Cretaceous rocks upon which the beds of the Potomac ment, Interior Department, Commerce Departrr°,nt, group were deposited. Possibly also some faulting or even flex Labor Department, Interstate Commerce Commisrion, ing has taken place, which would cause irregularities in the bedrock floor These local irregularities are described in as and Bureau of Engraving and Printing, the Penta ,^on much detail as data permit and are illustrated by a number of Building, Munitions Building, Archives Building, maps and sections. Apex Building, and others. Several hundred borel oles The boreholes that afford a basis for the altitude lines in the at these localities reached bedrock and afforded data maps and diagrams are about 600 in number, but not all of them were correctly interpreted by the drillers as to materials as to its altitude and configuration. Subsurface data penetrated or identity of bedrock. were also supplied for numerous sites in which bedrock was not reached, such as the Government Printing Office INTRODUCTION and some other buildings with deep-seated foundations. The District of Columbia region is underlain by In addition to borehole records supplied by Government gneiss or gneissic granite and schist, usually called agencies, subsurface information was contributed also "bedrock", which is at or near the surface in the western part of Washington but to the east slopes gently under 'Barton, N. H., and Keith, Arthur, U. S. Geol. Survey Geol. Atlasi, an eastward-thickening wedge of sands and clays of Washington, D. C.-Md.-Va. folio (No. 70), 1901. 2 Darton, N. H., Artesian-well prospects in the Atlantic Coastal Plain the Coastal Plain succession. At the east corner of the region: U. S. Geol. Survey Bull. 138, pp. 155-161, 1896. Darton, 1 T. H,, and Keith, Arthur, op. cit. District this bedrock surface is about 700 feet below sea 3 In acknowledging the sources of boring data, the Government agen level. Its position underground has been determined cies are identified by the names in use at the time the records were made available for this study The present equivalents of the offices cf the by borings at many places, and though the borings are Supervising Architect of the Treasury and Public Buildings and Grounds irregularly spaced and not all of the records are reliable, are the Public Buildings Service and National Capital Parks Serv'ce. BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA by well drilling companies and by owners of private gradational relation between sound rock, and rock that buildings. has been thoroughly disintegrated by weathering Much of the canvassing for data was done by me up to processes. 1940. Samuel Sanford obtained a few data in Mary Figure 1 shows the different datums a.nd also the land in 1905, and in later years R. C. Cady * and D. J. altitude of the bronze-plate bench mark in the Capitol Cederstrom, of the United States Geological Survey, Building, which is regarded as a standard datum collected information concerning some boreholes in marker. Virginia. Most of the altitudes of bedrock shown on plate 1 ALTITUDE DATUMS have been deduced by subtracting the depth reported The contour lines indicating bedrock surface on the by the driller from known altitude of the ground sur map, plate 1, are based on the "mean sea-level" datum face at nearby points. The altitudes in Washington established by the Coast and Geodetic Survey according are based chiefly on figures given by District of Colum to adjustments of leveling prior to 1929. The general bia or Army Engineers. As some of tH holes are adjustment of 1929 raised the datum plane 0.141 foot, slightly higher or lower in relation to sea level than is but this has been ignored because it would not affect indicated by such an approximation, the figure given the position of contour lines of surface or bedrock on on the map and in the tables for altitude of bedrock the present scale of the map. On the detailed maps surface at some holes may be subject to a correction of of parts of the District of Columbia and on the figures a foot or two. In wells outside of Washington the and smaller plates the datum is the one used on the altitude is taken from contour lines on th^ Geological original plat of the boreholes. The datum used by the Survey base map. In some places the tern "sea level" Engineer Department of the District of Columbia is is used in a general sense, or with refererce to "mean 0.846 foot above mean sea level (prior to 1929), and sea level" on the Geological Survey base map. that used by the Corps of Engineers, United States GENERAL GEOLOGIC RELATIONS Army, is mean low tide, which is 1.264 feet below mean BEDROCK sea level (prior to 1929). These slight differences in datum are insignificant in view of the natural irregu The bedrock that underlies the District of Columbia larity of the original bedrock surface and the entirely region is made up of crystalline rocks, principally granite, granite gneiss, schist, and diorite. Their +1.590- •+1.731' Mean high tide, U. S.C. and G.S. geologic age has been considered to be p^e-Cambrian (1901) (the oldest of the geologic ages), but no evidence has been cited to justify a positive age assignment. Most important for the purpose of this report is the fact that the crystalline rocks are much older geologically than

+ .705- +.846' Zero, D. C. Engineers any other geologic formations in the region, and their — +.715' Zero, Pennsylvania Railroad physical properties contrast sharply with those of the generally unconsolidated sedimentary formations found in the eastern part of the District. Wh^re the cry - +.238' Mean river level, U. S. C. and G. S. READJUSTED DATUM, U. & C. (1892-1901) stalline rocks have not been affected by weathering AND G. & (1929) H000' MEAN SEA LEVEL DATUM, U & C. processes, they are hard and either massive or slabby. AND G. S. (PRIOR TO 1929) The granite gneiss is described by Keith 5 as com posed mainly of quartz, feldspars (orthoclase and plagioclase), and micas (muscovite and biotite), with small amounts of garnet, chlorite, hornblende, tour maline, and pyrite. In places the rock contains scat tered segregations or "eyes" of quartz and other min

— - f.193' Mean low tide, U. S C. and G S. (1892-1901) erals. The rock is gray on fresh exposures, and its -1.405— — - 1.264 Mean low tide, (zero) U S A. Engineers I— -1.354' Mean low tide, U S. C. and G. S. (prior to 1692) generally slabby character causes it to breal* more easily 05 1 Foot parallel to the gneissic banding. Much of this rock could be termed "mica schist" where the mica content ELEVATION OF CAPITOL B. M. imparts a tendency to cleave parallel to the orientation U. S. C. ond G. S, prior to 1929------90685' DSC. and G. S, topographic survey of D. C.- - 69.958' of the mica flakes. The granite gneiss, including the U. S. C and G. S, 1929 general adjustment---90.544' D C. Engineers (zero for reference) — — — — — 89 840' schistose phases, is the most widespread of the crystal U S. Army Engineers, (zero) mean low tide— — -91.949' line rock types in the District. Quartz veins of vary FIGURE 1.—Diagram showing different datum planes used in the ing widths are common throughout the gneiss and Washington area. schist. Because quartz is resistant to disintegration by 4 Cady, R. C., Ground-water resources of northern Virginia: Virginia Geol. Survey Bull. 50, 200 pp., 1938. 5 Barton, N. H., and Keith, Arthur, op. cit. GENERAL GEOLOGIC RELATIONS weathering, large fragments of quartz may be en has removed the weathered material and the original countered at shallow depths where the enclosing rocks character of the various crystalline rock types can best are thoroughly disintegrated to a sandy soil. be observed in the Potomac gorge near Chain Bridge A large body of diorite underlies Georgetown and ex and along Rock Creek. tends northward to the District line. Where freshly exposed, the diorite is a hard, massive rock of dark gray SEDIMENTARY FORMATIONS/ color due to its hornblende content, which increases near Several unconsolidated sedimentary formations over contacts with other rock types. Fresh exposures are lie the crystalline bedrock in the District of Columbia uncommon and the soil which forms on the weathered area.6 Their general relations are shown in figure %, diorite is characteristically brownish-red. and they are described briefly below in order from Various younger intrusive bodies of granite have oldest to youngest. been identified among the crystalline rocks, A granite Potomac group.—The oldest of the unconsolidated with conspicuous biotite flakes extends along the west sedimentary formations in this area are of Lower side of Rock Creek Valley, notably in the valley of Cretaceous age and belong to the geologic unit krown Broad Branch where it has been quarried. Small len as the Potomac group. These sediments overlie the ticular bodies of soapstone and talc schist, which are the bedrock floor in a wedge-shaped mass that thickens metamorphic representatives of ultra-basic igneous rock rapidly eastward to nearly 1,000 feet. The sediir^nts types, have been identified in this general region. are varied in texture and color; sand and clay pre Because the crystalline rocks are so generally altered by dominate, in places occurring in separate lenses, but weathering, the various rock types are not easily more generally mixed in varying proportions. The identified and the present geologic picture of the basal beds, which are exposed at the surface in the crystalline bedrock is incomplete. western part of the area, are generally drab gray and The crystalline rocks are traversed by breaks or coarse, including gravel and arkose (coarse sand con cracks, called joints, which are especially conspicuous taining feldspar) derived from the disintegration of in quarries and ledge exposures but which extend far the old crystalline rocks. The basal beds generally underground. The joint system consists of two or more yield artesian water. The upper beds, which underlie sets of parallel fractures. The weathering of the rocks the eastern part of the area, include clays of a variety has been facilitated by the existence of these fractures of colors, chiefly pink, red, gray, and buff, and inter- which permitted the entrance of water into the rock bedded lenses of light-colored sand much of which is mass. cross-bedded. Local concentrations of iron oxide have The crystalline rocks lie at the surface in the north cemented the sands into discontinuous black bands thsit west part of the area. Their outcrop forms an irregu are generally less than an inch thick and very hard. lar northeast-trending belt roughly parallel to the The Potomac group is the most extensive of the sedi northwest boundary of the District (see pi. 1). For mentary units in the Washington area. Sediments of long periods during geologic time these rocks have been the Potomac group are naturally exposed on valley exposed to weathering and in places they are disinte slopes in a broad belt that includes all but the north grated to depths as great as 50 feet. In records of many western edge of the District of Columbia.7 Except in borings these weathered crystalline rocks have been the northeastern part, the exposures are discontinuous identified as "rotten rock". Natural exposures of sound rock are generally limited to the Potomac River 6 Barton, N. H., (Map of) Sedimentary formations of Washington, valley and its tributaries within the outcrop belt. The D. C., and vicinity, U. S. Geol. Survey, 1946. 7 Darton, N. H., Sedimentary formations of Washington, D. C., and cutting of these valleys below the general land surface vicinity, U. S. Geol. Survey, 1946.

NW. SE.

FIGURE 2.—Geologic section across the District of Columbia area, showing the succession and general relations of the principal sedimentary for mations. Kp, Potomac group (Lower Cretaceous) ; Kr, Raritan formation (Upper Cretaceous) ; Km, Magothy formation (Upper Cretaceous I ; Tc, Calvert formation of Chesapeake group (Miocene) ; QT, upland gravels (Pleistocene and Pliocene?) ; Qt, terrace deposits (Pleistocer<«>. •H s» a* i— i ^ B £T. o Bo^S^S, %**% **§ ^H^ & W&s-^ ^^ 8 g-|f-g. S^^S-g S |S | c?d§- I^B-cT ?3 3 B i 1 B :* KivPotomac andofmuch positsunderli B-Bfif??'! Alluviuma M. H*-I CD M« i-3 thrills>-! W ^ H— ' os Q. ° &j ^ "-« ^ ^ in ii ill ^ " i^LjS ® 55' 8: Is S- S o'Ê 0 ^^?? S^^ S- S- g 2 iTtrBâi H^^Q gL 3 ^CD ® ^g ^ § ^^g-crq jjaegi*S 03 03 — . 21 SO |_4 ^ CD _, ££ E±. S' PS Washington.downtown I &3 I s^ * £ mainlyits^tributariesareander H*3 s !"§•* 8- fill.artificialndThelowlandsa— area,OapitheMountPleasantie g|3> Ss'S|| § 8.3? s'l-: s,w^|l s^r ls;e i ? f| f *| &i if ^s es |-r-| -K 8 |i § 1 8. £ el!"! it* CD • £0 — « CD rr- rfl^lifytillt fl|i!ll^lî ;l4i^-llM^!l B. ^ fl g P g B- &0>B-r;-.g £ H & £3-0£°0£ Bi^="i.|Siîs.ff^|i.i;§;iiiifmM|sîffi m 2^«C? a> i?P^^^^S-ôi^g:5- :ggjQCDOS.-ô fD P®§0 ^'^ S^g-0§ g. ?+% ^^fDrS'MgS^jT 0 q B pPBog HhiBsogfljHsg CD 0 i-1 « j3 III Ed f^Mlf*^^>tgtoôrQ(•r^ rO KJ t~* • *•* ' M £ o4 o 1JB o Is ? 1 ? 1 ?, 1 i 1 E 1 ^ ?' 1 f ? Ill • White Oak 400- ,-y.,» ru.lij;».*vcT-^Jaî-£^ otcnûp^^^ Buena Vista Sea ,,'/ ^,',x •• •*•£ Gneiss ^->^ _. _____ fed/an Creek eL£/v O/1LC w£'-'- KT >.'-•/ v""-'i'' l ^ / ~ ^^ — ^"-^7" —\ — — _ C'ay' S3ncl (Po'omac group ) -400- 1 ;\ ,^ -^v.-'jx ^ (N 3< Glêiss ^'|\/ "T-— —— ——— — Potomacgroup Bedrock ' - ' ' K ' \ -\ M .\ "( s i -yG %^LTi-' FvC^"-'"-"/ J" v~ ~/ — r^ _ _ _ -800- ' ' < N ""'> ^n-^^^^^'j.,6"61"/ ^ C'/~-'

Section from White Oak southeast to Glen Dale, Md O Tenleytown WASHINGTON St. Elizabeths 400' » RateaU gravel Potomac group GEORGETOWN MONUMENT WASH | NGTONi D c . AIJAGOST,ôsp'ial Terrace cap Oxon Pun - - Silver Hill ______Plateau grayei cap __.,_ . "f OWS1_ § , j, r- YV-" 7^ '^ % ' "v ' ~7 ' ^/ -"* ' i : '^T^T— 'TTr^ ——y ——=———v— ____[] clay. send (Potomac group) ' ~* î ' - Gneiss -v 1 ., ^ | ^-î :"?r 7^— — — ^-_ — _ Potomacgroup -800- •1200- ^ * - —s ~^ ^ ' ) -^ ' T7; ^T^^T-^r-1 î . Section from Tenleytown, D C , to Meadows, Md

*oo4^——— _- Gravely H,gh terrace grave, on Potomac ^^^____^__^^^ K'VE^^^^^^^^^&^^^ , SMr % -"Gne,ss'' r ' level ' \ I l^--t\ ^ / -\--- |N /-,-Jy^, I -_;,-^._ ._ | ___ — __ _ Potomacgroup "|| -""""'• ..o-"-= u ...... ,.u.^«-^^ -400- i Gneiss ^ v'/ •• ' ^ Cf-' O --_S~T-,— r — ~— ;————_____ Cay, sand ^Potomac group) 7 x ' '/ •/-•-', ~^>: ''' ~^"/~ r> —s7--r- _ KT Upper Crefaceous and Tertiary clay sand, and marl ' -'^l-/*. •'/~.~, Gneiss ~.-( - '~t -~ ~i ~~ — — -r _ _ __ -1200- —————————————————————— Section through Munson Hill and Alexandria, Va., and Oxon Hill, Md. 1 0 2 Miles

FIGURE 3.—Sections acr" & the Coastal Plain-Piedmont overlap in Maryland, District of Columbia, and Virginia, showing relations of bedrock floor. GENERAL GEOLOGIC RELATIONS and the flats on both sides of the Potomac and Anacostia ^information is available. Such irregularities are the Rivers. Some of the lands bordering the rivers are the product of the events that comprise the geologic his result of artificial filling by man. The tidal flats along tory of this area. The eroded surface of the bedrock the Potomac and Anacostia Rivers, the wide area of formations was irregular at the time the earliest sedi the National Airport, and the lower parts of Potomac ments of the Coastal Plain were deposited. Erosion in Park were reclaimed by filling. more recent geologic time was responsible for addi tional irregularity as, for example, the removal of ths BEDBOCK CONTACTS sedimentary formations of the Coastal Plain sequence GENERAL RELATIONS by an ancestral Potomac River above the present sits In most drilling operations and excavations to reach of the Tidal Basin. bedrock in the District of Columbia region, the over Owing to the low rate of the eastward slope of ths lying materials are found to be the gravel, sand, and formations of the Potomac group, the basal contact arkose of the Potomac group near the western margin with the crystalline rocks ascends very gradually ths of its outcrop area; the various river-terrace deposits; interstream ridges to the west. Exposures of the lower the alluvium in the lower lands along Potomac River; deposits of the group extend eastward on a low grads wash on slopes; and extensive fill by man, notably in down the valleys leading out of the Piedmont region. the low areas formerly occupied by tide marsh. Many small outliers are left on the gneiss highlands to Under most of the city of Washington and area to the west. the east the bedrock is immediately overlain by gravel, The boundaries given on plates 1 and 2 are basecl on sand, and in some places clay, of the lower part of the detailed mapping of geologic contacts. The contact of Potomac group, as shown in figure 3. To the west, the Potomac deposits with the bedrock was rer.dily however, where the bedrock floor rises to sea level and located at most points, but during Pleistocene time above, the Potomac deposits were deeply trenched and there was much terracing at different altitudes along widely removed by erosion in later Cretaceous, Tertiary, the overlap zone of the Potomac basal beds. As a and Quaternary times, and in consequence the bared result some of the terrace deposits seem to be indis rock surface in some areas is overlain by sediments tinguishable from the much older gravels and sands of younger than those of the Potomac group, as shown the Potomac group that they overlap. This is espe in figure 4 and plates 5 and 6. cially true where the terrace materials were derived The general slope of the bedrock surface beneath the from nearby Potomac beds. Where arkosic materials sediments is between 100 feet and 150 feet per mile exist the deposits have been readily classed as Potcmac, toward the southeast, as shown by the subsurface con especially if they lie on a floor with pronounced slope tours on plate 1, but the rate varies locally. Although to the east. Ordinarily the gravel of the Potomac the generalized picture shows an evenly sloping plane group contains more vein quartz and fewer quartzite surface, closely spaced borings at individual building pebbles and boulders and is finer-grained than the ter sites reveal irregularities in the surface where detailed race deposits.

200' Mount Pleasant terrace FLORIDA '\VPmey Brane/i^S^y^'-. •..;::.:••••;•. -•^^.^.,^^.'Trva VENUE ^"e*^^P^^ CAIRO HOTEL SCOTT 100- MONUMENT "' Cl^- l/-''X~T~x'^'-^r^^^^ WHITEWH HOUSE Bedrock - - - i x 1 , ^ -( ^, V*^= ^gfSg?%w^^^^ MEMORIAL POTOMAC Sea level - I -R/VER •'jy^'-TjfrT^^r^J^-^f-^V^ River deposits -100-

-200'.

w. « -^ GEORGETOWN I STffEETS N.E. Filhpr- Sea /eve; - Clay, sand, gravel (Potomac group) -100'- V/-.0 c iT' *>""?/"' r^^^^dl^1^ - - '---vBedrock^-05^=7^- """-v ''V5;-;v>^ -200'- ^-C->~-T>-_.

-300'- B 2000 4000 Feet D. C. datum FIGURE 4.—Sections through Washington showing relations of bedrock and overlying formations. A, North to south along Sixteenth Street; B, West to east from Georgetown to Fifteenth and E Streets NB. 6 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA TENTJBYTOWN RIDGE local variation of rate and many small irregularities of On the Tenleytown ridge west of Rock Creek, which contour. The Potomac group on the Tenleytown ridge is followed by Wisconsin Avenue, an extensive outlier may be 40 feet thick near Calvert Street and the Naval of arkose (feldspathic sand) and gravel of the Potomac Observatory, but it thins to the north and disappears group lies on the floor of crystalline rocks. This floor in the northwestern part of Cleveland Park. On slopes from an altitude of 350 feet on Wisconsin Ave Ordway Street near the line of Thirty-first Street the nue near Quebec Street and on Massachusetts Avenue basal material is a thick bed of coarse gravel. near Forty-second Street, to 240 feet on Thirty-ninth Street just north of T Street and to 210 feet a short BBIGHTWOOD TO SILVER SPRING distance south of the United States Naval Observatory. On the ridge extending north from Brightwood to Small outliers cap the high summit near Fortieth and Silver Spring the Potomac deposits lying or the granite- U Streets, the ridge on Foxhall Road north of W Street, gneiss floor are thin and mainly of interest as a source the hill at the Bureau of Standards, and other high of water supply for shallow wells. Many basal con summits near Military Road, notably at Fort De Russey tacts with bedrock have been exposed, but at some places and knolls north and south. there is doubt as to the identity of the beds called Poto Much of the material of the Potomac group in this mac, owing to the presence of terrace deposits. Near area is gravel, as shown in plate 3, A, but in places this the District line and farther north near Silver Spring, grades into or is overlain by arkosic gravelly sand, the highest ridge is capped by gravel that is believed distinctively Potomac. The Potomac group is overlain to represent the old high plateau (Pliocene? and and overlapped by the fine-grained buff sand of the Pleistocene), which here attains an altitude of 350 feet. Calvert formation (Miocene), which in turn is capped Much of the Potomac in this region is gravel without by the orange loam gravel of the high plateau (Plio special character, but in places it grades into or is over cene? and Pleistocene) that forms the smooth surface of lain by feldspathic sand, and it also grades into sandy the ridge to its abrupt termination at an altitude of clay. The plane of contact with the bedrock slopes 410 feet at Tenleytown. The principal relations are southeastward with apparent regularity from the alti shown in figure 5. Some of the finest exposures of this tude of 350 feet south of Silver Spring to 300 feet near

2000 D. C. datum FIGURE 5.—Section along Wisconsin Avenue from Tenleytown to Potomac River. succession formerly were to be seen in cuts on Wisconsin Walter Reed Hospital, to 250 feet near Takoma Park Avenue, Tunlaw Road, and Calvert Street, all on the railroad station, and to 200 feet in the valley half a mile ridge now occupied by Mount Alto Hospital, part of east of Brightwood, a rate that continues far to the which is shown in plate 3, B. There were other good east. exposures of the Potomac gravel and arkose in the higher parts of Cleveland Park; at the north end of TAKOMA PARK TO PAINT BRANCH the ridge on Foxhall Road near an altitude of 340 feet; From Takoma Park eastward to Paint Branch the on Woodley Road; on Fortieth Street just south of western part of the Potomac deposit forms a gently Calvert Street; on the Naval Observatory ridge and in eastward-sloping upland that is deeply trenched by the ridge followed by Wisconsin Avenue, notably on valleys. The gravel, the sand, and locally the clay lie the west side of Wisconsin Avenue just north of Hall on a nearly plane surface of the bedrock, which slopes Place; and in cuts on Thirty-seventh Street near U eastward at a uniform rate. This surface is not a Street, Whitehaven Parkway at Thirty-fifth Place, and perfect plain however, but presents low mounds and along the small stream west of the Naval Observatory. shallow valleys. Near Lewiston, it has an altitude of At most of these places the contact of gravel on the 220 feet; it goes under the surface at -Paint Branch at gneiss was visible. This contact slopes down to the an altitude of about 90 feet; and at Branchville it is southeast at a rate of about 100 feet to the mile, with about 100 feet below sea level. GEOLOGICAL STJRVEY PROFESSIONAL PAPER 217 PLATE 3

A. GRAVEL OF POTOMAC GROUP ON GNEISS. North side of Harvard Street, 200 yards east of entrance to Zoological Park, 1928. Looking north.

B. PLATEAU GRAVEL (PLIOCENE?) ON CALVERT FORMATION (MIOCENE). Arkose of Potomac group just below. Tunlaw Road north of Calvert Street ,on line of 38th Street 1894 GEOLOGICAL SURVEY PROFESSIONAL PAPER 217 PLATE 4

TERRACE DEPOSIT OF CAPITOL HILL. About 250 yards south of the Capitol. Top of terrace is 80 feet above sea level. Geologist stands on the underlying Potomac group. GEOLOGICAL SURVEY PROFESSIONAL PAPER 217 PLATE 5

A. TERRACE GRAVEL AND LOAM ON GNEISS. N Street near 24th Street, NW. Much of the older part of the city is built on the river terrace deposits. To the east these deposits lie on sand and clay of the Potomac group.

B. TERRACE DEPOSIT CAPPING ARKOSE NEAR BASE OF POTOMAC GROUP. Cut on east side of 16th Street at Meridian Hill Park, 1900. Later concealed by wall. Top of terrace is 205 feet above sea level. GEOLOGICAL SURVEY PROFESSIONAL PAPER 217 PLATE 6

A. FAULT ON EASTERN EDGE OF ZOOLOGICAL PARK. Adams Mill Road near Clydesdale Place, 1925. Looking northwest. Fault is between gneiss and terrace gravel.

B. FAULT IN REAR OF CALVERT STREET NEAR ZOOLOGICAL PARK. Terrace gravel and loam on gneiss, 1901. Looking north. East side had dropped about 2 feet. GENERAL GEOLOGIC RELATIONS

LOWER PART OF WASHINGTON supposed river deposits lie directly on the bedrock as In the western part of the city of Washington the much as 90 feet below sea level. surface is a succession of sloping terraces at different BOCK DECAY altitudes, ranging from the Mount Pleasant terrace (altitude about 200 feet) to the lower terraces in down The granite, gneiss, schist, and other crystalline town Washington (altitude 100 feet and less). The rocks that crop out in the northwestern part of the relations are shown in figures 4 and 5. The basal rela Washington area and underlie the Costal Plain sedi tions of the conspicuous terrace deposits on which the ments to the east are exposed in some places as very Capitol is built at an altitude of 80 feet is shown in hard ledges, especially along such recently cut gorges plate 4; the basal contact of the Mount Pleasant ter as those of Kock Creek and the Potomac Kiver. Much race deposits is shown in plate 5, B. of the rock at the surface, however, has been long ex An excavation at the southeast corner of Seventeenth posed to the weather and penetrated by surface waters and I Streets exposed gray arkosic sand overlain by and is "decayed" or "rotted" to a considerable depth. terrace gravel, which caps the I Street ridge and is cut This decay has reduced the rock to a compact sand, off to the south by an overlap of clay of the next lower mostly very micaceous. The disintegrated condition terrace on the downward slope to the south. Deep cuts is irregular in depth and degree, but in wide areas the near the corner of Eighteenth and E Streets for the rotten rock breaks down into a sandy soil or becomes so building of the Department of the Interior exposed ter soft that it can be worked with pick and shovel and race deposits lying on gravelly sand of Potomac aspect. would not be recognized as rock by most persons. In most of the areas from 30 to 100 feet above sea Even where soft, however, this material shows the. ori level west of Twentieth Street the Potomac group is ginal mixture of component minerals. In general, the absent and the bedrock is overlain by terrace deposits. decayed rock is somewhat porous, so that it will com The western edge of the Potomac group in this part of pact materially under heavy weight. In excavating the city, as determined from scattered data, is shown on for foundations, much of the softer decayed rock must plate 1 by a broken line. Many street cuts and excava be removed if it is necessary to reach material tjiat tions from Constitution Avenue to T Street have re might be classed as "solid rock." In parts of the region vealed terrace deposits lying immediately on the gneiss. covered by Cretaceous or Tertiary deposits and Pleisto (See pi. 5, A.) Contacts were exposed in cuts west of cene terrace gravel some of the old decayed rock was the corner of Nineteenth Street and Jefferson Place removed by erosion in earlier geologic times, but this (between M and N Streets); at 1210 Twentieth Street; condition is local, and pits and borings througl the on M Street between Twentieth and Twenty-first; at younger coverings ordinarily reveal a considerable Twenty-first and O Streets; at Twenty-first and P body of decayed rock before hard "ledge rocl'" is Streets; and at the intersection of Twenty-first Street, reached. No prediction can be made as to the thichness Massachusetts Avenue, and Q Streets, where a 2-foot of decayed rock or its strength. bed of gray sand lies on the gneiss. At 2107 Pennsyl DEFORMATION vania Avenue, 12-foot pits reached bedrock ("decayed gabbro") under terrace gravel. Doubtless the bedrock floor under the formations of In its later stages of development the Potomac Kiver the Coastal Plain has been flexed and broken to some eroded deeply into the bedrock and stripped off much extent at different geologic times, but evidence as to the of the earlier and later terrace deposits as well as the course and amount of such flexures and faults is diffi remaining part of the western margin of the Potomac cult to obtain. Since the widespread leveling of the group in a wide, deep trench. In this trench the land in early Cretaceous time the region as a whol?- has Potomac deposits are cut through nearly as far east been uplifted and depressed many times. The general as the Highway Bridge and to depths considerably trend of these movements has been along northeast- below present sea level. This depth of erosion is indi southwest axes, but there probably has been much local cated by the fact that, even at the Jefferson Memorial, variation in trend and amount. SW. NE. r200' Arkose

-150'

-100'

Bedrock L

500 500 Feet FIGURE 6.—Section across fault at Eighteenth and California Streets NW., looking north. 8 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA At the beginning of Potomac deposition, some old to 60 feet) including some thin lenticular bodies of fault scarps may have remained, causing local breaks gravel. All these probably are river-terrace deposits. in the bedrock, which now appears to slope regularly No Potomac strata were recognized but it is likely that eastward. Erosion also produced many local ridges some of the older strata lie deeper on the bedrock floor, and valleys. The uplifts and submergences of the Coast though no suggestion can be made as to their limits. al Plain in later Cretaceous, Tertiary, and Pleistocene The borings were made by the George Drilling Co., and times must have been attended by flexing and faulting, the records were furnished by the Procurement Division which would affect the position of the bedrock surface, of tjie Treasury Department. but few such features are revealed. A few faults in NATIONAL, ARCHIVES BUILDING bedrock and overlying strata have been observed in the western part of Washington, but the displacement is Nineteen test borings were made by Battle Bros, at small and apparently the faults are rather short. the site of the Archives Building between Seventh and Along one fault exposed in a trench on Eighteenth Ninth Streets and Pennsylvania and Constitution Street near California Street, where arkose of the Avenues. Nine of them, from 90 to 120 feet deep, pene Potomac group rested on gneiss, there was a drop of trated bedrock to a depth of 5 feet. The other 10 were 40 feet or more on the east side. (See fig. 6.) sunk to a uniform altitude of —60 feet (D. C. datum) A fault, probably local, in the terrace deposit on and ended in sand, clay, or gravel. The location of the Adams Mill Road (see pi. #, A) has a throw of about 8 boreholes and the altitude of the bedrock surface are feet. Another small fault was formerly exposed in the shown on plate 7, which gives also an interpretation of north side of the alley just north of Calvert Street. (See the bedrock configuration by 5-foot contour lines. pi. #, B. ) These exposed faults suggest that others may Data from a 628-foot boring made many years ago in be present under covered areas. the old Center Market on Seventh Street near the corner of Constitution Avenue are added. DISTRICT OF COLUMBIA As shown in the two cross sections (pi. 7), consider NORTHWEST WASHINGTON 8 able diversity of materials was revealed by the holes, GENERAL GEOLOGIC SETTING but fine sands and clays predominated. The upper materials were fill and river deposits, but the deeper In the northwest section of Washington, crystalline holes penetrated compact sands and gravels, most likely rocks are exposed at the surface in approximately the of Potomac age. Hole 4, in the northeast crmer of the western half. The rocks are difficult to identify in most site, entered fine, compact sand at a depth of 43 feet of the area due to deep weathering and soil cover, but and continued in this material to a basal b^d of sand, they are well exposed in the Potomac River gorge above gravel, and boulders 6 feet thick lying on bedrock at Georgetown, and along Rock Creek. In the high area including Cleveland Park, Tenleytown, and American 103 feet below sea level. A similar succession was found in hole 7 in the center of the area. In hc^e 15, near University is a large outlier of sedimentary formations which are entirely surrounded by, and underlain by the southwest corner of the site, the sand and gravel crystalline bedrock. East of Rock Creek and the Wal was underlain by 35 feet of sand and some clay, all fine and compact, on bedrock at —74.2 feet. In hole 16 ter Reed Hospital grounds a practically continuous the fine compact sand extends from —38 feet to bed cover of sedimentary formations overlies the bedrock. The greatest variety of foundation conditions are found rock at —78 feet. Hole 17 had 30 feet of soft blue clay in the northwest section of the city. The table of bore in its upper part, with fine sand and gravel and fine hole data at the end of this report lists the bedrock sand (all compact) for the next 34 feet. In hole 18 altitude at many locations, and the subsurface condi clay and sand extended from the surface to a depth of tions at several building sites in the northwest section 30 feet below which were 3 feet of sand an^j gravel, 6 are described below. feet of soft sandy silt, and 42 feet of compact sand and clay and sand, to bedrock at — 77% feet. Hole 19 pene APEX BTJIUDING trated 40 feet of fill, clay, sandy silt, and thin deposits The site for the Apex Building between Sixth and of gravel, underlain by 54 feet of very compact fine Seventh Streets, Pennsylvania Avenue and Constitu sand, on hard clay with some thin gravel streaks in the tion Avenue, now occupied by the Federal Trade Com upper part, and reached bedrock at —868 feet. It mission, was explored by six holes about 70 feet deep, seems probable that these compact sands and clays and with their bottom from 58 to 62 feet below datum. the local basal gravel represent the lower part of the None of the borings reached bedrock, which here lies Potomac group. between 105 and 115 feet below datum. The materials INTERNAL REVENUE BUREAU BUILDING penetrated were clay (15 to 25 feet) containing vivianite grains of bright green color, and clay and sand (50 In 1926 nine holes were bored into mica schist at the site of the Internal Revenue Bureau Building, between 8 See also table, pages 35-36. Tenth and Twelfth Streets, and Constitution Avenue NORTHWEST WASHINGTON 9 and C Street, under direction of W. C. Lyon, of the Of vania Avenue. So far as it goes it affords excellent fice of the Supervising Architect, Treasury Department. foundations for such buildings as the Star, Raleigh, They showed that the bedrock surface is very smooth Harrington, and Warner. How much these buildings and nearly at an altitude of —60 feet (D. C. datum), have settled since their erection appears not to have declining to —64.7 feet in the southeast corner of the been observed. Doubtless they have all gone doT^n a area. The materials penetrated are shown in three cross very small amount, for a slight compaction was to be sections of plate 7. expected of the 30-foot thickness of sand and other OLD POST OFFICE BUILDING porous materials that extend to bedrock. The building now occupying the square between POST OFFICE DEPARTMENT BUILDING Eleventh, Twelfth, C, and D Streets, built in 1892, was About 20 test holes were bored at the site of the Post occupied for many years by the City Post Office. The Office Department Building, Pennsylvania Avenue be site was explored by eight boreholes, 20 to 30 feet deep, tween Twelfth and Thirteenth Streets, in 1931 and sunk in the bottom of an excavation about 15 feet deep. 1932. Many of the holes went to bedrock or to I was consulted as to the underground conditions and "refusal." 9 The borings were made by several com predicted bedrock about 70 feet below the surface. Ex panies and are not aH in close accord as to details^ but plorations conducted by Bernard Green, Architect of they indicate the configuration of the bedrock surface. the Library of Congress, revealed that in this area there One section on plate 7 shows some details in the Post was at a depth of 35 to 40 feet a deposit of sand with Office Department site and is continued south through gravel and boulders so compact that piles could be the site of the Interstate Commerce Commission Build driven into it only a foot or so. This stratum served ing, repeating records of holes 9 and 29, as given ir the as foundation for the old Post Office Building, the Eve two west-east sections through the buildings of the ning Star Building, and the north extension of the Department of Labor and Interstate Commerce C om- Raleigh Hotel (E and Twelfth Streets). In the plats mission. Some of the difference in names of materials it has been referred to as "bedrock", but true bedrock recorded is due to different drillers. lies considerably deeper. It extends some distance west A cross section from west to east across the center of Twelfth Street and served as foundation for the of the Post Office Department Building site, shown in Warner Building (formerly Earle) at Thirteenth and plate 7, was condensed from a section made in the office E Streets, and other buildings. On Eleventh Street of the Procurement Division in 1931. It shows hole its surface descends to —22 feet (D. C. datum) at the 16 reaching bedrock at —58 feet, but according to a south end of the Post Office Building and to —30 feet at record by the Mott Core Drilling Co. at this place the Pennsylvania Avenue. It rises to —21 feet at the gneiss was penetrated from — 60.7 to — 65.7 feet under north end of the Evening Star Building. a foot of "sandy shale." The overlying gravel bee1, 25 In a letter of April 18, 1898, Bernard Green wrote feet thick, made very hard drilling. me as follows regarding the Raleigh Hotel foundation: LABOR DEPARTMENT AND INTERSTATE COMMERCE "The piles stopped at a depth of 37 feet (below curb) COMMISSION BUILDINGS in hard material supposed to be rock, but a 4%-foot The strip of land occupied by the buildings of the caisson revealed a bed of large rounded stones closely Department of Labor and the Interstate Commerce packed and imbedded solidly in fine sand. The stones Commission, along the north side of Constitution Ave were dislodged by the crowbar only with difficulty, and nue between Twelfth and Fourteenth Streets, was ex so I adopted that bottom as practically equivalent to plored by holes from 60 to 82 feet deep bored by the solid rock for the purpose of the foundation." This Giles Drilling Co. in 1931. It was specified that all gravel and sand deposit was reached by the piles in the holes must penetrate bedrock for 3 feet, but as the south end of the Post Office excavation, as shown by penetration was made by a spoon no core could borehole 3 (pi. 7), and was conspicuous in borehole 1, be obtained. The rock samples called "Potomac in the northwest corner of the site of the Internal Reve gneiss" were so soft that they "decomposed in water." nue Building, where it was penetrated from 26 to 39% At nearly all the holes the overlying material for a feet (17.5 to 31 feet below D. C. datum). It was under few feet consisted of cobbles, boulders, and compact lain by nearly 29 feet of sand—gray above, greenish in sand, most of which showed considerable mica. the middle, and white below—which lies on mica schist Locally silt or clay lay on the gneiss. It is not known at 59.7 feet below datum and was bored into for 8 feet. whether any of these sedimentary materials represent A short distance south of this borehole the gravel thins, the Potomac group; at least the greater part appear to and apparently it is entirely absent near Constitution be river deposits. Two sections are shown on plate 7. Avenue at the site of the Internal Revenue Building, as The holes show a valley in the bedrock surface just shown in borehole 4. The bed probably is an old river deposit and occupies a channel, the middle of which ex 9 The term "refusal" is used where the drill points or piles encounter a very hard material that is practically impenetrable. Ordinarily it is tended from Tenth to Thirteenth Streets, near Pennsyl bedrock, but in some places it is a boulder or a stony layer. 10 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA east of the Department of Labor and a low ridge under "refusal" to boring at —23.5 in hole 4 and at —23 feet the northwest corner of the Interstate Commerce Com in hole 5. This appears to indicate the presence of an mission Building. The configuration of the bedrock underground ridge 10 feet in height under th e southwest surface presents considerable diversity, as shown by corner of this block. the 5-foot contours in plate 7. Constitution Hall, on the next square south, and the Other holes bored in part of this area in 1932 and a building of the Pan American Union beyonc1 it are built blueprint of some of the old holes show some slight on piles, and no data have been obtained as to the under differences in character and limits of materials and of lying bedrock surface. depth to bedrock, but these discrepancies appear not to be important. INTERIOR DEPARTMENT BUILDIITG A very complete exploration was made of the under COMMERCE DEPARTMENT BUILDING ground conditions at the site of the new building for the. Most of the boreholes made to test the underground Department of the Interior on the two blocks extending conditions at the site of the building for the Depart from C to E, Eighteenth to Nineteenth Streets. (See ment of Commerce, Fourteenth to Fifteenth Streets, pi. 8.) It consisted of 46 holes 50 to 70 fee* deep most E Street to Constitution Avenue, passed through 70 to of which were extended into the gneiss bedrock, and 90 feet of unconsolidated sediment to the bedrock floor. several test pits. The gneiss is overlain by gravel and Several records of holes are given in condensed form in sand and a thick body of clay, as shown in the sections the two cross sections shown in plate 7. It seems prob on plate 8. The exploration was done in 1935 under able that the lower deposit of sand and clay with some the direction of Mr. C. E. Darnall of the Office of the gravel at the base is of Potomac age, at least in part, and Supervising Architect of the Treasury, and I examined that the overlying gravel, clay, and mud are deposits the samples obtained. The location of hoV-s and the of the lowest terrace or of a deep part of the trough of configuration of the bedrock surface are shown on the the old Potomac River, which was excavated consider map and sections. (PL 8.) The principal contour ably below present sea level in this area. The artificial line, at —30 feet, indicates some slight diversity of con fill is no doubt correctly identified in the records, but figuration, notably a narrow valley in the southeastern apparently its lower limit is not indicated in every part of the area and small hills 5 to 7 feet Hgher than borehole. The blue clay at a depth of 20 feet contains the valley bottom. In general the bedrock presents a numerous scattered grains of the green mineral vivian- remarkably smooth shelf cut on the gneiss surface in ite, a characteristic feature in this general region. pre-Potomac time, for the lower part of the gravel and AMERICAN NATIONAL RED CROSS BUILDINGS sand apparently represents the west edge of the Poto mac group. Part of this gravel and sand vas exposed On the block between Seventeenth, Eighteenth, D, in the excavation for footings and cellar, but its identity and E Streets, test borings were made for the Memorial was not recognized with certainty. The w'de shelf of to the Women of the Civil War, commonly called the bedrock appears to extend some distance to the south Eed Cross Building, the World War Memorial Build and west. ing, and the office buildings of the American National Red Cross^ They are shown in figure 7. 17TH STREET BETWEEN PENNSYLVANIA AVENUE AND H STREET Four holes drilled in March 1914 showed the follow ing conditions under the main Red Cross Building, in In December 1941, six holes were bored to and into the east end of the block: bedrock at and north of the Court of Claims Building, in square 167, east of Seventeenth Street between Penn Altitude of land surface and bedrock surface under Red Cross sylvania Avenue and H Street, to ascertain foundation Building conditions for a heavy building. A predict'on that the No. of Location Land sur Bedrock (feet) bedrock was from 65 to 75 feet below the rurface was bole face (feet) closely verified by the results of the borings, given in 1 23.25 At -31.3. figure 8. 2 27 At -34.8. 3 24.3 From -34.2 to -36.2. The land surface slopes up from an altituc'0. of 55 feet 4 24.6 From -37 to -39. at the south to 67 feet at H Street. The main slope of the bedrock beneath is to the south, probably with The contours of bedrock surface show a low under local irregularities. The gravel and sand and clay ground ridge with its axis under the northwestern part penetrated undoubtedly constitute the edge of the Poto of the main Red Cross Building. A slight down-slope mac group, as revealed in the deep excavation for the to the northwest may reach —40 feet near E Street. Hill Building, on the ridge at Seventeenth and I Streets. The "heavy gravel under blue clay" in holes 4 and 5 at These are overlain by terrace deposits laid down by the south end of the site of the Red Cross Office Build an earlier Potomac River. Of the total thickness of ing appears to be underlain by mica rock, which gave sediments penetrated by these holes, 60 to 6^ feet deep, NORTHWEST WASHINGTON 11

CORCORAN ART GALLERY

/ STREET

JL--^') AMERICAN NATIONAL RED CROSS

-32.8* • Bore hole, showing altitude O Bore hole, showing altitude -12' (Not to bedrock)

STREET

DAUGHTERS OF THE CONSTITUTION HALL MEMORIAL HALL °NPILES) (°NP'LES' AMERICAN REVOLUTION

STREET

RED CROSS 44 3lilLDli?G '*™ REOFFICESS % WOMENS WORLD WAR MEMORIAL STREET HOLE 1 HOLE 8 HOLE C HOLE B HOLE A BUILDING A 30'- £ / A Fill Fill ;V.Sand ~~T 20*- Sand, clay~7 = Gravel, brown Cinders — ICIay Clay, bouldery Gravel, clay-3 Fill with cinders Fill 10'- Brown f« Cinders gravelly " .-.Sand Sea level clay 2' •;'. :::•.-, "Sand- (D. C datum] %? 'C -10'- Boulders, Sand, clay sand, and _ __r f\ ^* gravel —— :• Clay, sand. gravel -20- Sand, liver mud _, -— "^ -*• Sand, gravel -30- -TO^v^i?-^ Gravel, brown .^ . „....=;.*• . tLi^r^' rj /-> Bedrock/ x ^.'J,"o'a .*„"' -36'.., ; , c Bedrock ~-/\'i

B 100 0 100 Feet I , , , 1 —— 1 FIGUEH 7.—Map and section showing configuration of bedrock surface and boreholes on the site of buildings of the American National Bed Cross, between C and E, Seventeenth and Eighteenth Streets NW. 8S88&8—50———2 12 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA

A . HQLe „ HOLE 1 "OLE 6 A 60'-, 50- Clay, some sand, 40- Clay, sand Clay, some sand 30- — 20- — _ _ — — Sand, gravel 10'- Sand, gravel Sand, gravel - ___San_c1 ._ cTay___ Sea level- \-7C7 7^' ^/ iV;"x \ -4.3' ^ Sand, fine gravel x •- r -•-' -'• •' ^ l^''^'^ '\~s ^ ' N"'^ - ' - - 0. -18.6'^ x \ Bedrock x -lo.s' Bedrock

17TH STREET

COURT OF CLAIMS BUILDING

50 100 Feet

D. C. datum FIGURE 8.—Boreholes and configuration of bedrock surface on east side of Seventeenth Street between Pennsylvania Avenue and H Street NW. From data by Gilbert Brooks, 1941. Figures on the map indicate the position of bedrock in relation to sea level. about half may be Potomac group trenched by the old on terrace deposits composed of sand, gravel, muck, valley of Potomac River to within 25 to 30 feet of the and clay. The terrace materials were deposited in a bedrock. How far south of Pennsylvania Avenue the wide trench cut into the bedrock by an earlier Potomac Potomac group extends is not known. River. Plate 8 shows the location of boreholes and Besides showing the position of the bedrock surface altitude of bedrock, and the probable configuration of the holes afford data as to the character of the overlying the bedrock surface is indicated by contour lines. The deposits. Hole 6 reported considerable coarse sand most noticeable feature is a shallow basin which may and gravel from a depth of 32 to 53 feet, and hole 1 extend north to and beyond C Street anc? east under was in sand from a depth of 38 to 50 feet. Hole 3 the southern edge of the Interior Department Building. penetrated a mixture of gravel and sand from a depth The borehole data for this area were supplied by the of 42 feet to bedrock 58 feet deep, and hole 4 from a drillers, Sprague & Henwood, of Scranton, Pa., through depth of 32 feet to bedrock at a depth of 65 feet. The the Procurement Division of the Treasury Department. top of the bedrock was "soft" for the first foot in holes 1 and 4, for 3 feet in hole 5, and for iy2 feet in hole 6. 20TH ANI> 21ST STREETS, C AND D STREETS The rock was penetrated 10 feet or more in all six holes. At the site of Temporary Building 4, on square 87E, between Twentieth and Twenty-first, C ard D Streets 19TH AND 20TH STREETS, CONSTITUTION AVENUE AND C STREET NW., 7 test holes were bored in 1930, from 34 to 56 feet Eight holes bored at the site of the buildings for deep, all but 1 of them to bedrock. In 1940 14 holes the Public Health Service, later occupied by the Atomic were bored in the south half of this block to afford Energy Commission, in square 128, between Nineteenth detail as to underground conditions for a proposed ex and Twentieth Streets, Constitution Avenue and C tension of the Federal Reserve Building; these holes Street, penetrated gneiss at a depth of about 50 feet. were from 44 to 77 feet deep and penetrated the bed The area is covered with fill 22 to 25 feet thick, lying rock floor for a few feet. Cross sections si owing most NORTHWEST WASHINGTON 13 of the features are included on plate 8. The data were notable feature is a 20-foot valley in the center of the furnished by the Corps of Engineers, United States block. The relations of the boreholes are further Army. A notable feature in the east half of the block shown in the cross sections on plate 8^ Hole 6 passed is the slope of the bedrock, which evidently marks the through a bed of boulders from a depth of 37 feet to its edge of a low ridge extending from the west. bottom at a depth of 47 feet without reaching bedrock,

FEDERAL RESERVE BOARD BUILDING which doubtless is not far below. This bed represents part of the filling of the buried valley. Iii 1935 12 test holes were bored at the site for the Federal Reserve Building, between Twentieth and NATIONAL ACADEMY OF SCIENCES Twenty-first Streets on 'Constitution Avenue; 11 of At the site of the National Academy of Sciences them penetrated the gneiss bedrock and indicated the Building, between Twenty-first and Twenty-second configuration of its surface, as shown on plate 8. A Streets, Constitution Avenue and C Street, four test

FIGURE 9.—Map of area south of Constitution Avenue and west of Fourteenth Street SW., showing configuration of bedrock surface. 14 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA borings were made in 1922 which penetrated bedrock probably continues under Constitution Avenue from from 6 to 18 feet. In every hole the upper part of the Twenty-third to Eighteenth Streets, af shown in rock was found to be considerably decomposed. The figure 9. overlying deposit was reported as clay and sand 6 to 28 feet thick, the thickest part being under the southeast NAVY DEPARTMENT BUILJ5ING corner of the building. The fill, mostly of sand, was Part of the area on the south side of Constitution 5 to 10 feet thick, the smallest amount being in the Avenue between Seventeenth and Twenty-first Streets southeast corner. The location of the holes and eleva has been explored by boreholes. Most of these holes tion of bedrock are shown in plate 8. The bedrock reached bedrock, as shown in figure 9, which shows also surface slopes rather steeply to the southeast probably the configuration of bedrock in the area expending past from an underground ridge extending from the north the Reflecting Pool, Washington Monument, Jefferson west, as suggested by the broken contour lines in plate Memorial, and Highway Bridge. Cross sections in 8. This downward slope to the southeast and south figure 10 show borehole data under the Navy Depart-

HOLE 13 HOLE 14 HOLE 6 HOLE S HOLF 7

Sand, mud Fil1 Cinders, sand Cinders, sand Cinders, sand, mud _ jPFi" (bfick rtc) . . • ;•••. Sand, light - dband, some mica -f^felS Sand, fine Sand, muck Hfc*Sand coaree Sand, gravel, .jome mica . ——— _ _<5.Sf&uraveJJarge .,__ —— 1| — Micaceous sand 7 w^^-J.-^W^*'^'——— "--'^'—— ' ' Bdrock - - ~ ————— ^^«k-

JSand Cinder^ fSand, some clay | San<1' *•* Marsh mud i^r< Sand, muck , fine ,-Sand,., . , w B VP, . . . U. S. A. Engineers datum FIGURE 10.—Sections through boreholes at site of Munitions Building and Navy Department Building, 1918. A., 350 feet south of Constitution Avenue; B, 600 feet south of Constitution Avenue.

HOLE 5 HOLE 9 HOLE 3

Sea level -

-10'-

-20-

-30-

HOLE 6 HOLE 2

Fill Fill Fill Sea level - Sand, medium ~^~"~~—— — Silt Silt, fine sand -10- Sand '""•---^_ Peat Peat Peat -20- .v.-Sand, clay,' gravel .'- •^•^^Ss^ss -VC rpj^TVTTtT-^f^ -22 7' ' -} '-^B d V"'k^'^CN/ ' -20-4'--i ' l S^-^'^^'JTi^i5':!*'*Jiiiiiii y^.'HarjTsa'ricl, gravel 1 ^ v. e roc •' ^ - X-"" x "''/- /C'> ^-'24^1/vB7drock> B 50 0 50 Feet U. S. A. Engineers datum FIGURE 11.—Sections at northeast corner of Navy Department Building. B is about 75 feet south of A. NORTHWEST WASHINGTON 15 ment, at Eighteenth Street and Constitution Avenue, cinders, sand, and clay, which extends to the surface. and the Munitions Building just to the west, and those The blue clay is part of an extensive deposit occupying in figure 11 represent a later series of holes bored in the a wide area in the lower western part of dowrtown northeast corner of the Navy Department area prelimi Washington, and the vivianite is conspicuous through nary to repairs necessitated by serious subsidence. out. The member of sand and gravel above this blue The area west of Twenty-first Street between Consti clay appears to lie on an irregular surface eroded by tution Avenue and Lincoln Memorial has not' been ex the running water of a predecessor of the Potomac plored, but it is evident that there is a general down River. grade of the bedrock surface south from the Academy of Sciences, where it is near sea level, into the basin 1ST STREET NEAR R STREET AND FLORIDA AVPNTJE a short distance east of the Lincoln Memorial, where the altitude of bedrock is —41 feet. As shown in A 122-foot hole at 1620 First Street NW., near R figure 9, the rock surface east of the longitude of Street and Florida Avenue, office of the Fairfax Farms Twenty-first Street forms a wide platform at an alti Milk Co., penetrated rotten rock at a depth of 42 to 46 tude of —22 to —32 feet. The bedrock at the east end feet below sea level. of the Reflecting Pool and under the southeast corner Hole at 1620 1st Street NW of the Navy Department Building is higher than —20 Feet feet, indicating an underground "ridge" of considerable Clay, yellow, brown, and blue——————_—————— 0-41 prominence. Sand with some water—_———————————————— 41-74 It seems probable that in all of this area, as well as in Clay, blue______————— 74-02 much of the area north of Constitution Avenue shown Sand with water______—_——_———————— 92-101 Clay, blue______———_—————————— 101-109 in plate 8, the Potomac group is absent or is repre- Water sand—___—__—___.——_———————————— 109mi8 , sented by only a thin remnant of basal gravel and sand. Rotten rock______——__— 118-122 Most if not all of the material revealed by excavations or borings appears to be a river deposit laid down after 4TH STREET AND PENNSYLVANIA AVENUE a wide trough had been excavated by an earlier A test hole drilled at the corner of Fourth Street and Potomac River to a depth of more than 40 feet below Pennsylvania Avenue, at the site of the proposed present sea level. Municipal Center, had the following record: STATE DEPARTMENT BUILDING Borehole at J^th Street and Pennsylvania Avenue NW The building at Twenty-first and Virginia Avenue r-xt now occupied by the State Department was erected for Clay, yellow sandy_———————————————————— 0-21 Clay, yellow, with gravel—————————————————— JTL-41 the War Department in 1941. In the two squares be Clay, gray with bits of black wood and gravel———— 41-54 tween Twenty-first and Twenty-third, C and D Streets Clay, sandy, yellow-———————————————————— 54-62 about 60 test holes and pits were sunk in the autumn Sand, gray, water————————————————————— fJ-74 of 1938, affording the data given in plate 8 and figure Clay, gray, light on dark, with some gravel and black 12. The most marked feature is the rapid rise of bed wood ______——_——-———————————— 74-103 Clay, sandy, gray_—___————————————— 1C3-107 rock near the line of Twenty-second Street from D to Sand and gravel, blue-gray, water———————————— 107-115 C Streets. Rock was revealed in a 4-foot cut at Clay, sandy, greenish blue, some gravel————————— 115-137 Twenty-second and C Streets and extended up Twenty- Sand, coarse, water_———_———————————————— 1F7-145 third Street to a point opposite the old Naval Hospital Clay, sandy, with gravel near base——————————— 145-157 Building. East of Twenty-second Street, except in Clay, gray, with gravel and wood———————————— If7-l74 Clay, greenish blue and "rotten rock"————————— 174-176 hole 38, the bedrock was not identified by core samples, Rotten rock______—————1——————__——— 17"W.79 but it is highly probable that where the drills showed "refusal" to drive they had reached the bedrock floor. The altitude of the land surface at this place is r.bout In all the area where this floor lies 30 feet above sea 20 feet, and the surface of the bedrock probably i? at a level it is overlain by a body of blue clay believed to be depth of 174 feet, or 154 feet below sea level. a river deposit of Pleistocene age. The clay is more JUDICIARY SQUARE than 40 feet thick in places and thins out to the west against the upward slope of the rock floor. The min In February 1936 three groups of test holes were eral vivianite occurring in this clay in small amount is bored in Judiciary Square, between Fourth and Fifth, conspicuous by its bright-green color and glistening D and F Streets. They were on the site of court build aspect. Above the blue clay is a terrace deposit of sand ings and mostly about 40 feet deep. Holes 9 and 15 and gravel, which contains considerable clay in places were deeper, and the drillers suggested that they and is overlain by a mantle of brown sandy clay averag reached bedrock at depths of 125 and 132 feet, respec ing about 15 feet in thickness. Next above is a fill of tively. It seems likely, however, that the holes were 16 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA

Borehole, with number po« Borehole, probably to bedrock

Trench in rock \ C STREET

FEDERAL NATIONAL ACADEMY OF SCIENCES RESERVE

2/sr STREET . HOLE 9 A

, ' i _: ,—~7~r~ "•"•", t, =-.aana,gravei rock^ ~ * <• ' ~J,'i1_'-24"P TTrrTv^. r>

B23 o Sand, gravel, B' £ TREET Cla y STREET 2, ST 50- ._,.! • HOLE 51 HOLE 52 HO L i______L. 40 L rr^ , !]____ ^rr^T^, —— ~f'" Terrace cap x -1-r^ '^Gne\s,!T. lix"^!"/ 1> I '--/ " x " v ^ V(^ls =>, ^~?-^.^ — „ ^a"ndy clay, Clay, brcwn sandy 30- FSand, — gravel ^o __^^ Bedrock^l'i^ gravel _ X ' V22 Coarse sSllJlp Sand, gravel, clay gravel-""^ 20- if^-S^S ~ ~^^*-v-; Cr ay, blue Clay, blue 10- "'?^ (Vrvianite)

Sea level - v/ -^-TT-}; '^JxV.r T 3~T^r;~-~- -10- ' " - ' -P_ l ^Be'drock\1 ' PV-^ .-'',' -' P j -- , \ , r/7W N ' - \ ' ^ -.- ~-\ •-, ^

ID C datum) FIGURE 12.—Map and sections at site of State Department Building, between Twenty-first and Twenty-third, C and D Streets N"*7"., 1938. The 10-foot intervals on the map show the thickness of overburden beneath the natural ground surface; they are not contours. NORTHWEST WASHINGTON 17

discontinued about 50 feet above the bedrock. The Record of well in basement of Harrington Hotel records are as follows: Feet Clay, blue______'______-__—- 0-28 BoreJiole 9, near center of east side of Police Court Gravel, coarse, and boulders_————————————————— 28-45 Clay, sandy, green_———_————————————————— 45-46 Feet Loam and clay______0-5 Sand, medium fine, grading down into coarse sand and1 Sandy clay______5-14 gravel______———————————— 46-57 Sand, coarse______14-47 Clay, blue, tough______————_—————______57-72 Sand and gravel______47-60 Gravel, medium fine, yields 180 gallons a minute—_——— 72-83 Do ——————————————______60-73 11TH AND G STREETS Sand and boulders______73-75 Blue clay, hard, greenish______75-85 The record of the 97-foot hole at the northeast corner Sand and clay, some gravel______85-95 of Eleventh and G Streets, formerly Palais Koyal, now Sand and clay, bluish______95-105 Woodward & Lothrop North Building, gives sand and Sand, coarse, bluish, compact______105-115 Sand, greenish, very compact, some clay______115-125% gravel at 2Q to 40 feet on "crystalline formation," under lain at 80 feet by "gravel or disintegrated crystallines" Borehole 15, near center of Juvenile Court extending to the bottom. This record might indicate Feet that the bedrock was entered at 3 feet below sea level, Loam and clay______0-4 but records of other nearby holes indicate that the bed Sandy clay______4-12y2 rock here should be expected at about 70 feet belcw sea Sand, coarse, light colored______12^-53 Sand, coarse, and gravel—______—_—__ 53-73 level. Sand, fine and gravel______72-83 14TH AND R STREETS Clay, sandy, hard, greenish blue______83-93 A borehole at the building of the Chesapeake & Po Clay, sandy, hard, bluish______93-103 Sandy, medium, bluish white______103-123 tomac Telephone Co., at the northwest corner of Four Sand, fine, white, wood______123-132 teenth and R Streets, revealed the following: Much of this material is of Potomac age beginning at Borehole at northioest corner of 14th and R Streets N~*r. a depth of 75 feet in hole 9 and at 83 feet in hole 15, or Feet even higher. Clay, yellow on blue______—__ 0-21 Clay, brown sandy______——_—_————_ 21-27 6TH AND 7TH STREETS, O STREET BETWEEN Clay, yellow, grading down into bluish-green sandy clay with gravel______27-53 A well on O Street between Sixth and Seventh Streets Sand and gravel, coarse, with some clay in the middle penetrated rock at a depth of 100 to 201 feet. part ______53-83 Clay, bluish green, and gravel______83-98 Record of lower part of well on O Street 'bettoeen 6th and 7th Soft "rotten rock" grading down into "very hard Streets NW. rock"______98-110 Feet Soapstone______100-135 14TH STREET NEAR IRVING STREET Talcose slate______135-142 Hard soapstone______^______142-192 A hole at the store of the G. C. Murphy Co., 3128 Gneiss and quartz______192-201 Fourteenth Street, between Irving Street and Park Road, started at an altitude of 192 feet and passed 10TH STREET BETWEEN D AND E STREETS through rotten rock from 82 to 102 feet. Hard rock A report on a well at the old building of the Washing may be at an altitude of about 110 feet above sea level. ton Gas Light Co., 417 Tenth Street, in 1935, was as follows: Borehole at 3128 14th Street NW. Feet Record of iveU at 417 Tenth Street NW. Clay and gravel (terrace cap)____——_————____ 0-28 Pine sand and clay—__—______———————— 28-41 Feet Clay, yellow, and sand, fine______—_—_____ 41-47 Clay and gravel——————_—_———————————____ 0- 8 Clay and sand, gravelly——_____—————————__ 47-54 Clay, blue, stiff__—______—__——_____ 8-18 Sand, gray______—————___————————____ 54-53 Clay, brown, sandy______18-29 Clay, tough______—______58-71 Sand and gravel. Water supply_————————__—_ 29-45 Sand and gravel (at base of Potomac group)-———__ 71-82 Clay, sandy, blue______45-56 Rock, rotten______82-102 Sand ______—______56-61 Clay, blue, stiff______61-65 MAYFLOWER HOTEL, AND VICINITY Sand and gravel_————______65-76 Clay, black, stifL.______76-77 Many street cuts and other excavations in the lower part of Washington in the vicinity of Seventeenth Street 11TH AND E STREETS have exposed the deposits lying on the gneiss and other A well at the Harrington Hotel, E Street between crystalline bedrock, and these deposits have been pene Eleventh and Twelfth Streets, had the following record: trated by many borings. (See fig. 13.) One of the 18 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA s.

t2 PAN tt f <0 NAVY tjS AMERICAN «D. A. R. « AM.RED ^ 46.5_ DEPT. UNION Q CROSS Terrace deposits _ _ _ _ _ —•

Arkose (Potomac group)

500 500 Feet FIGURE 13.—Section along Seventeenth Street from Constitution Avenue to DeSales Street, looking west. most notable exposures was in the large excavation Cuts along L Street between Fifteenth and Sixteenth made in 1922 for the foundation of the Mayflower Hotel Streets (1929), notably behind Nos. 1527-1529, showed (originally called Walker Hotel) on the north half 2^2 feet of arkosic, cross-bedded sand, mostly gray of square 162, bounded by Connecticut Avenue and (apparently the Potomac group) overlain by a coarse Seventeenth, L, and DeSales Streets.10 This excava boulder bed at the base of the terrace deposit. Deep tion was 35 to 40 feet deep in a filled area, the average excavations (1926) on the west side of Seventeenth altitude of which was 57 feet. The gneiss was found Street halfway from I to K Street exposed light-gray at an altitude of 19 feet above sea level (D. C. datum) cross-bedded arkosic sand of typical Potcmac aspect at Seventeenth Street and sloped upward to the west under 14 feet of terrace deposit (boulders at base, loam to an altitude of about 21 feet at Connecticut Avenue. above), with a sharp plane of separation. Cuts on the Its surface was nearly smooth. south side of K Street at Nos. 1758-1762 showed 3 feet The gneiss is overlain by about 7 to 12 feet of the of typical arkose under brown-red gravel and boulders basal deposit of the Potomac group, which consists of of the terrace deposits. An 8-foot trench on M Street micaceous gray arkose, mostly gravelly, and grades into west of Seventeenth Street showed gray and brown a mixture of sand, gravel, and boulders. Some angular sand very much like Potomac arkose under terrace masses of schist in the lower part are 1 to 2 feet long. gravel and boulders, and these deposits wore exposed The upper part of the Potomac group is mostly gray also on Nineteenth Street just south of K Street. None sandy clay. Next above is a deposit of light-brown of these excavations, however, was sufficiertly deep to silt, 6 to 9 feet thick, filled with organic matter, includ reach bedrock, the top of which in this vicinity lies near ing numerous large stumps of bald cypress, some of sea level. which were rooted in the top of the underlying sandy clay, and others were scattered at higher levels. These SOLDIERS' HOME indicate the presence of an ancient swamp. There Several wells bored in 1892 at the puirp house in were many wood fragments and a general admixture Soldiers' Home at an altitude of 209 feet penetrated of peaty plant material and numerous seeds, all classed bedrock, samples of which were examined by me. In as Pleistocene by Berry. A large diatom fauna deter one hole soft rock grading down into hard rock was re mined by Mann was classed as pre-Kecent. The swamp ported at a depth of 163 to 173 feet, and hard "nigger- deposit was overlain by 5 to 15 feet of sandy gravel, head" rock from 174 to 478 feet. Well 2 reported soft sand, and loam, at the top of which was a very thin layer of old soil. Above the old soil was 10 feet or rock at depths of 173 to 175 feet under greenish clay, more of artificial fill. and well 5 reached rock at a depth of 165 feet under The fossil-wood horizon was found also in an excava greenish clay with water-bearing satnd at th^ base. tion for Stoneleigh Court, at the corner of Connecticut I/SDECKEJR TUNNEL Avenue and L Street, 100 yards south, and in another hole made long ago on the west side of Connecticut The aqueduct tunnel passing under Washington not Avenue at M Street, about 100 yards northwest. far north of Florida Avenue to the McMillan Keservoir, known as the Lydecker Tunnel, was entirely in crystal »°Wentworth, C. K., Berry, E. W., Mann, Albert, and LaForge, Laurence, The fossil swamp deposit at the Walker Hotel site, Connecti line rock. Several shafts from the surffje exposed cut Avenue and DeSales Street, Washington, D. C.: Washington Acad. contacts at the top of bedrock. At the east shaft on Sci. Jour., vol. 14, no. 1, pp. 1-42, pis. 1-4, 1924. Hay, O. P., On the geological age of the Walker Hotel swamp deposit in Washington, the west side of the McMillan Reservoir, dark coarse D. C., and on the origin and the ages of the Coastal Plain terraces in chloride rock merging down into chloritic gneiss was general: Washington Acad. Sci. Jour., vol. 14, no. 12, pp. 255-264, 1924. entered at a depth of 102 feet. The shaft was sunk at NORTHWEST WASHINGTON 19 the bottom of a 40-foot bluff of gravel, sand, and clay. Avenue are thinly capped by terrace gravel and sr»nd, The land surface was at an altitude of 131^ feet. The and the smooth surface of the terrace is not broken by record, obtained in 1884,11 follows: the fault. In the Widows Mite air shaft just north of East shaft of Lydecker Tunnel at west side of McMillan Wyoming Avenue, near the line of Twenty-second Reservoir Street, the official section shows a capping of "clay and Feet sand 30 feet thick" underlain by 35 feet of "clay," but Clay, red and mottled blue and gray under sand this is undoubtedly a mistake, as the gneiss has I>a«?-n (Potomac) ______0-35 Clay, sandy, mottled———______35-40 revealed by many cellars in this vicinity under only a Sand, some clay, some lignite, pyrites______40-65 few feet of terrace gravel and sand. In the air s^aft "Kaolin," sandy with thin layers of irony conglom on the highest part of the ridge near the corner of S erate ______65-71 and Thirty-fifth Streets the blueprint of the tmnel Clay, blue gray______71-80 section shows 42 feet of "clay" lying on "soft rock" at Sand, clayey, red, blue, and gray streaks______80-87 Sand, mostly white, red at base______87-90 a depth of 158.7 feet, but in fact the rotted bedrock out Clay, blue-black, compact, sandy below______90-95 cropping extensively in that area is overlain by very Sand, mostly white______95-102 thin remnants of terrace gravel at 195 feet above sea Rock, soft, dark, coarse, chloritic; top soft, then level. Probably the clay referred to is mostly rctten blasted ______102-148^ rock.

Figure 14 gives a condensed reproduction of a cross PINEY BRANCH RELIEF SEWER section along the Lydecker Tunnel, compiled from a blueprint in the office of the Corps of Engineers, United The Piney Branch relief sewer follows Arkansas States Army. It has the datum of mean high tide. Avenue from the vicinity of Decatur Street northeast (See fig. 1.) This section indicates that bedrock was ward to Ingraham Street, where it curves eastward and entered at an altitude of 29.5 feet at the east shaft, at continues beyond Fifth Street. It is a 9^-foot tunnel 43.62 feet at the Thirteenth Street air shaft,12 and at in bedrock from the vicinity of Gallatin Stree* to 85.28 feet (a depth of 45 feet) at the Champlain Ave Seventh Street. The geologic relations as found by nue shaft, a few rods south of Kalorama Koad. The wash borings and in the course of its construction by official section does not show the fault with a displace the District of Columbia Department of Sanitary En ment of about 40 feet that was exposed in 1931 in a gineering are shown in figure 15. trench on Eighteenth Street at California Street. This Nineteen holes were bored on the line of this tunnel. trench showed typical arkose of the Potomac group on Their records report sand, clay, and in places gravel the east side of the fault and gneiss on the west side. on the decayed rock, but except under Ingraham Street The gneiss is exposed for some distance up the slope to from the vicinity of Ninth Street nearly to Fifth Street the west, where it appears to be overlain by arkose, all this material is valley fill and decayed rock and not which probably does not extend quite to Nineteenth the Potomac group. At Eighth and Ingraham Streets Street. The arkose and gneiss west of Champlain a hole entered "very soft decayed rock" at a depth of 10 feet, under compact sandy clay and compact sand 11 Robinson, Thomas, The strata exposed in the east shaft of the water-works extension (abstract) : Washington Philos. Soc. Bull., vol. (doubtless Potomac), to a contact with bedrock at an 7, pp. 69-71, 1885. altitude of 200 feet (D. C. datum). In the next bore 13 According to the driller of this hole, "dark blue 'soapstone" was reached at a depth of 80 feet, which is close to 65 feet above sea level. hole, 300 feet farther east, the very soft, decayed rock

Sea level -

Datum mean high tide FIGURE 14.—Section along Lydecker Tunnel from the vicinity of Foundry Branch east to McMillan Reservoir. Corps of Engineers, United States Army. 888898—50———4 20 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA

Curve to east under Ingraham Street

SCl Sandy clay S Soft decayed Sg Sand, gravel f Firm de-ayed 125' g Gravel h Hard rock 500 o 1000 Feet I I I I 1 1______I______1 FIGURE 15.—Section along Piney Branch relief sewer, northeast along Arkansas Avenue and east along Ingraham Street NW.

is overlain by 18 feet of soft sandy clay on compact surface of fully 15 feet, some of which, however, is part clay sand with bedrock contact at an altitude of 180 of the general southeasterly slope. A tnried valley feet. A hole just east of Seventh Street reached soft, about 10 feet deep passing north-northeast and south- decayed rock at 13 feet below the surface, or at an alti southwest through the center of the site is a marked tude of 172 feet. These holes passed through soft, feature. decayed rock to "very firm rock," the surface of which SOUTHWEST WASHINGTON M slopes eastward. A short distance down the slope to the east the bedrock was covered by only a thin body of GENERAL GEOLOGIC SETTING valley fill, under which it was conspicuous in the sewer The Southwest section, the smallest division of the trench. It is difficult in this area of sand and gravel city, presents the least variety in its geologic setting. to distinguish valley fill from the gravel at the edge The entire section is covered by geologically recent river of the Potomac group unless one is familiar with their terrace deposits and artificial fill. The depth to bed character and knows their relations. rock ranges from 50 to 300 feet except at the Reflecting CALVIN COOLIDGE HIGH SCHOOL Pool where it is about 25 feet deep. The subsurface con The site for Calvin Coolidge High School at Fifth ditions in this section are generally characterized by a and Tuckernian Streets, was explored by 18 boreholes predominance of fine-grained sediments, r, high water to bedrock. They passed through from 20 to 40 feet table, and a large proportion of area covered by arti of the marginal sediments of the Potomac group, ficial fill material. mainly gravel and sand with some clay admixture in Several deep holes in the Southwest section have places. The holes revealed some diversity of configura reached bedrock, or by failing to reach it hs.ve delimited tion of the bedrock surface, which is shown in figure its position. Wells at Twelfth and C Streets and at 16. At the southeast corner there is a descent of this Fourteenth and D Streets reported "roclr" very defi nitely. The 202-foot hole at 623 D Street reported rot ten rock at the bottom at —174 feet, unexpectedly deep, but possibly the rock was entered at less depth. There was a report that the 208-foot hole at the old power house, 41/2 and O Streets, reached bedrock, below —196 feet, but no evidence was furnished. Th°. 207%-foot hole at Half and T Streets was perhaps 100 feet too shallow to reach bedrock. The report of bedrock in the 146-foot hole at Second and E Streets and Virginia Avenue undoubtedly was an error.

RAILROAD BRIDGE The bridge over the Potomac River for the railroads to the South crosses from the foot of Fourteenth Street SW. In planning this bridge to replace tr?. old "Long Bridge," several holes were bored to test the foundation conditions. Hole 5 at the northern abutments was en 100 Feet tirely in sand, gravel, and clay, mostly if not all river FIGURE 16.—Map showing configuration of bedrock at Calvin Coolidge deposits, to an altitude at 122^ feet below mean low High School, Fifth and Tuckerman Streets NW. Borings by N. C. Wyeth, 1937. Altitude of land surface, 247.4 feet; top of fireplug at southwest corner, 258.68 feet (D. C. datum). 13 See also table, pages 36-37. SOUTHWEST WASHINGTON 21

Bridge floor +13' (U.S.A. Datum) WASHINGTON. D C

FIGURE 17.—Section across Potomac River at railroad bridge, showing boreholes by Southern Railway. (Datum mean low tide.) tide. Hole 2, in the bottom of the river near the central WASHINGTON MONUMENT pier, entered bedrock at about 102 feet below sea level It is popularly supposed that the Washington Monu and penetrated it for 6 feet. A section along the line of ment is built on bedrock, but this unfortunately if not the bridge is given in figure 17. true. Its foundation, a mass of concrete about 37 feet The red clay and hard white sandy clay in hole 3 are thick and 126% feet across, lies on sand and gravel very likely part of the Potomac group, and the lower about 65 feet above the bedrock floor. This sand and beds in holes 2, 4, and 5 are also probably of that age. gravel member is separated from the bedrock by 10 to The main body of sand, gravel, and mud, however, was 30 feet of blue clay. In 1898 there was a project to deposited by the Potomac River millions of years later place concrete piers under the original foundation after that stream had cut its wide, deep trench during down to bedrock, but after adding to the foundation the later part of the long-continued general uplift of and placing under it a concrete collar 13% feet thick it the region. was thought that sufficient stability had been secured, HIGHWAY BRIDGE notwithstanding the yielding nature of the underlying deposits. These already had permitted 5*4 inches of In planning to replace the old Long Bridge over sinking from 1879 to 1898, but with widened base the Potomac River borings were made in 1903 to ascertain amount of subsidence from 1900 to 1930 was only about the underground conditions. Three holes reached bed 0.6 of an inch. The Monument was also made nearly rock from 84 to 110 feet below mean low tide, and five vertical. The load with enlarged foundation is slightly others were sunk nearly to bedrock. The results, kindly more thai?81,000 tons, of which the shaft weighs close to furnished by the Corps of Engineers, United States Army, are shown in figure 18. Besides defining the 44,200 tons, or a total of nearly 5 tons to the square foot. position of bedrock they show a body of river mud 75 The relations of bedrock at the Monument have been feet thick near the northeast abutment and 60 feet thick determined accurately by two series of boreholes made near the center of the river. Farther southwest this by the Washington Monument Committee. The inner mud gives place to sandy materials, probably by inter series is about 100 feet from Monument, and the outer mingling, for all are river deposits. The lower part of series is about 400 feet from it. The location of: the the section is sand and clay with locally a mixture holes and the altitude of bed rock are shown in figure 19. of gravel, probably in part at least of Potomac age. Some wider areal relations are shown in figure 9.

-40'

FIGURE 17.—Section across Potomac River at railroad bridge, showing boreholes by Southern Railway. (Datum mean low tide.) 22 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA

U. S. A. Engineers datum Mean low water FIGURE 19.—Map and sections near Washington Monument. Based on boreholes by Washington Monument Committee, 193C and 1931. SOUTHWEST WASHINGTON 23 The 15 test boreholes about the Washington Monu ment passed through gravel, sand, and blue clay. At the top is a thick mantle of terrace sand and gravel. The basal beds lie on a low ridge of bedrock. The thick body of the blue clay is regarded by the engineers as a river deposit. "Partly petrified wood" in a thin layer was reported at 47 feet below sea level in bore hole 3 (inner series), about 100 feet due west of the Monument, and a thin layer of decayed vegetal matter was penetrated 4 feet below it lying on a foot of white sand. Next below is blue clay, here only 12 feet thick, lying on soft bedrock at — 62% feet. "Old wood" was reported at —59 feet on the blue clay in hole 7 (inner series), about 100 feet southwest of the Monument. In hole 4 (inner series) "petrified wood" occurs in sand 8 feet above the bedrock, which is at — 55.2 feet. These occurrences of vegetal materials are all suggestive of the Potomac group but not proof of its presence, for in places wood occurs in the Pleistocene deposits. The blue clay, regarded as Pleistocene in age, is widespread in the general region of the Monument and was exposed extensively in the adjoining northwest section in exca vations at F and Fourteenth Streets, Thirteenth and E Streets, E Street between Thirteenth and Fourteenth Streets, Eleventh Street and Pennsylvania Avenue, and _-3JL7'______X___ fJ>_^_Lj----L.--^ 7' the blocks between Twenty-first and Twenty-third, C \ \ ^-\*^/ I /Q. X , Bore hole, showing altitude of and D Streets. Holes 1 and 5 (outer series) penetrated bedrock below meanJow tirfe

"mica rock" for 20 feet. Holes 1, 3, 4, and 5 (inner 50 Fe-;t series) penetrated "soft rock" grading down into hard rock for 20 to 25 feet. Hole 2 (inner series) reached FIGURE 20.—Map showing configuration of bedrock surface at Lincoln blue clay at —32 feet, under about 36 feet of sand and Memorial. Based on boreholes by Corps of Engineers, U. S. Army. X, Center of building. Broken contour lines are hypothetical. gravel, and penetrated it 8 feet to within about 15 feet of the bedrock. Hole 6 (inner series) reached blue WATER GATE clay about —27 feet. Hole 8a (outer series) was in blue clay from —23 to —58 feet, with a small amount The site for the Water Gate, just west of the Lincoln of gravel and mica at base. Memorial, was explored by 69 probings and boreholes by the Corps of Engineers, United States Army. LINCOLN MEMORIAL, These, together with results of other boreholes tc the Twenty holes were bored to ascertain the position of east and north, are presented in generalized form in the bedrock floor at the site of the Lincoln Memorial figure 22. at Twenty-third Street. The area was about 200 feet The Water Gate area is in a trough cut through the square, on reclaimed river flat with average surface Potomac group into the bedrock in later geologic time elevation of 16 feet, and the holes were from 42 to 56 and floored by gravel, sand, and clay in irregular bodies feet deep. (See fig. 20.) The material penetrated was deposited by the river. A few years ago the surface mainly river mud down to bedrock. The relations of was a level tidal flat, which was reclaimed later by a tliis area to the Water Gate on the west and Reflecting cover of fill. Pool on the east are shown in figures 9,21,22, and 23. These data afford a basis for drawing contour lines 011 the bedrock surface and a cross section from the REFLECTING POOL, Water Gate to a point a short distance east of Wash Eleven holes were bored by the Corps of Engineers, ington Monument. (See figs. 22 and 23.) United States Army, to determine the nature of ma A conspicuous feature in this area is the rise of the terials under the site of the Reflecting Pool, which lies bedrock surface as a ridge of considerable prominence east of the Lincoln Memorial. The holes are in two with highest known point of —17.6 feet in hole 2, at the lines about 80 feet apart and spaced at intervals for southeast corner of Rainbow Pool, just west of Seven nearly half a mile. Some of the features and relations teenth Street. Its summit may be higher than this are shown in figure 21. east of borehole 2, but the bedrock surface descends into 24 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA w. E. 21 ST STREET 20TH STREET I9TH STREET I8TH STREET lff"° LE " HOLE 9 HOLE 7 Surface of reflecting pool HOLES HOLE 1

0- 10- 20' -18' _ _ _ _ _ — ,— «r^- -XT )T7' C '-!- 30- _ i -*i -» ^ x - -34.8' -^ ^, ^w———— W -30. 7 ' \ /— / (, Bedrock ^ ^ }\^ ^ -213 t''-*. - ' \^ ' -* 40- ^

1Q' HOLE 10 HOLES HOLE 6 Surface of reflecting pool HOLE 4 HOLES HOLE 2

0- 10'- 20- ____^-,-cr^i7.3 I, 30' T V/"^^' X -/ -^ X ~ ._ r->T^'-~T O ' -31' '~ N 'i V — ~7 ' \>' -~; ' >~; ' -^na.' ^'^' v 'i s-'.---/- s -' ,, 0 A ' ,," i _\ / - ' • • -• 40- __——— Bedrock ' ' \ / - <- \-32 6 - ^ / -39.5'1'/, N /-^ 50- r-, J ~~ / N "**

300 300 Feet U. S. A. Engineers datum Mean low water FIGORB 21..—Sections under Reflecting Pool, east of Lincoln Memorial, showing position of bedrock surface. A, near north margin of pool; B, near" south margin of pool, 80 feet south of A. Holes 10 and 11 are about 600 feet east of the center of the Memorial.

Boreholes to bedrocK.with altitude in feet below mean low tide

Contour lines broken where hypothetical

500 Feet I____I____I____L FIGURE 22.—Map showing configuration of bedrock surface around Lincoln Memorial and Water Gate. Based on boreholes by Corps of Engineers, U. S. Army. Contour lines by N. H. Darton. SOUTHWEST WASHINGTON 25

V * &'UlUlUlSUlWW & & S S S S «i, £ £ £ ^ £ * £ S U> U) " °> " °> WASHINGTON

>-43.2 l«-38.4 X 0-36.3

• Core drill holes;figures are altitude of bedrocK surface below mean low tide ° Probings

wsw ENE.

Water -20- -40- '•'^^^^i^^__ __ 7 ______-______-——— - — -•> _. -60- -80'- -100'.

500 500 Feet U. S. A. Engineers datura FIGURE 24.—Plan and section across Potomac River at Arlington Memorial Bridge, showing probable configuration of bedrock surface as revealed by boreholes at abutments and piers. Broken lines are hypothetical contours. Based on boreholes and probings by Arlington Memorial Bridge Commission, 1925. to

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rn •s^ »O O /7TH STREET a « NORTHEAST WASHINGTON 27 Some of the holes to bedrock in the southern part K penetrated bedrock between depths of 159 and 225 of the Jefferson Memorial area appear to have passed feet below sea level with its top at —79 feet, and a 159- mostly if not altogether through river deposits. The foot hole at 18 O Street reported bedrock at —100 feet. average depth of the holes near the memorial was near The 300-foot hole at Fourth and F Streets shows that 100 feet, with the bedrock surface ranging from 80 to bedrock is below —225 feet at that place.

90 feet below sea level. The top materials were fill and 1ST STREET JUST NORTH OF M STREET river silt, "mud," and sand, mostly of fine grain, but there was coarser "sand" and "gravel" near the bottom One hole at Chapin-Sacks Co., on First Street just of most holes. Very little clay was reported as such. north of M Street, was reported to have penetrated I should hesitate to class any of the material as Potomac granite from 197 to 210 feet, and another hole, "150 feet group either from its character or from any theory as south," reported "hard rock" from 145 to 208 feet (indi to probable maximum thickness of river deposits. cating bedrock surface altitudes of —150 feet and —103 feet, respectively). A difference of nearly 50 feet AGRICULTURE DEPARTMENT BUILDING within so short a distance seems improbable, and the A boring made in 1938 at Twelfth and C Streets, for record of the deeper hole may not be reliable as to the the building of the Department of Agriculture, reported position of the top of the bedrock.

"blue rock" at 89 to 90 feet, which indicated that here 7TH STREET BETWEEN A AND B STREETS the bedrock surface is close to 53 feet below sea level, a The following record of a well drilled in 1940 for high place in the bedrock surface. The following rec the Chesapeake & Potomac Telephone Co. Exchange, ord was furnished by the Washington Pump & Well Co.: on Seventh Street between A and B Streets, shows the Boring at Department of Agriculture Building, 12th and C position of bedrock overlain by the lower formation of Street* SW. the Potomac group. Feet Soil and clay______0-26 Borehole on 1th Street between A and B Streets NE. Clay, yellow, and gravel______26-39 Sand, medium fine, some clay______39-49 Sand, gravel and clay, brown (terrace deposit on feet Sand, coarse, and gravel______49-58 Potomac group)_____—_—_————————————— 0-105 Clay, brown-______58-63 Clay, blue______105-158 Sandy clay, brown__—______————————— 158-175 Sand, brown______63-69 Sand, coarse, and gravel______69-84 Sand and clay, blue______175-197 Clay, blue, tough______197-242 Clay, blue______84-89 Rock, blue______89-90 Sand, water______242-256 Clay, blue, tough______—— 256-272 FEDERAL, BUILDING SITE BETWEEN 11TH AND 14TH Sand, water______272-288 STREETS, C AND D STREETS Clay, blue, tough______—————_— 288-307 A series of test holes was bored in 1935 at the Federal Sand and gravel, water______——__—————— 307-328 Granite (top at—261 feet)._____———————————— 328-331 site between Eleventh and Fourteenth, C and D Streets. The holes varied in depth from 22 to 58 feet, the deepest 15TH AND E STREETS ending about 65 feet above bedrock which was reported The old 365-foot hole at the Hygienic Ice Wo^ks, to be 85 feet below sea level in an old well at Fourteenth started at an altitude of 50 .feet, encountered rod: at and D Streets. (See fig. 25.) The records are of in 300 feet below sea level, and penetrated rock for 15 terest because they indicate the materials constituting feet. The water-bearing gravel here is probably rear the river terrace. the base of the Potomac group.

NORTHEAST WASHINGTON 14 Well at 15th ana E Streets NE. Feet GENERAL GEOLOGIC SETTING Sand, fine______————————— 0-20 Throughout the Northeast section of the city the Clay and sand, gravel streaks——_—————————— 20-50 crystalline bedrock is overlain by unconsolidated sedi Sand, fine, white, with wood—__——————_—————— 50-53 Clay, white and red (red, 95-128 feet)————————— 53-135 mentary formations. The depth to rock ranges from a Sand, full of water______—_————————— 135-159 few feet around Takoma Park to about 800 feet at the Clay, white and red______——————— 159-184 east corner of the District. Various deep holes have Sand and clay, mixed———————————————————— 184-212 reached bedrock, and other holes not deep enough to Clay, dark blue, tough______— 212-216 reach rock have delimited its position. The data re Sand and clay, some gravel streaks——————————— 216-240 Clay, sticky, sandy streaks————————————————— 240-256 ported show the general southeastward slope of the rock Clay, dark, very tough———_——————————————— 256-260 surface. The 162-foot hole at Lincoln Koad and S Clay and sand______————————_—__ 260-272 Street, reported "talcose rock" at —38 feet. The 150- Clay, dark, hard______—————————————— 272-274 foot hole at U Street between Fourth and Fifth re Clay and sand mixed, light lead color—————————— 274-298 ported rock at — 43 feet. A 225-foot hole at Fourth and Pebbles and sand, conglomerate streaks——————— 298-320 Not given______——————— 320-350 14 See also table, pages 37-38. Crystalline bedrock__—_————————————————— 350-365 888898—52———3 28 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA WASHINGTON TERMINAL CO. figuration in the region northwest of Woodridge and The deep wells of the Washington Terminal Co. at near Hyattsville. the Ivy City shops all end in gravel, indicating that the SOUTHEAST WASHINGTON 15 bedrock here lies deeper than 162 feet below sea level. One hole had the following record: GENERAL GEOLOGIC SETTING Hole at Ivy City shops of Washington Terminal Co. The Southeast section of Washington ir similar to Feet the Northeast in that unconsolidated sedimentary for Clay, red___^______0-43 mations form a continuous cover over bedrock. The Clay, blue——______43-72 depth to rock ranges from about 300 feet ne

WOODRIDGE Three holes for St. Elizabeths Hosptal reached gneiss; two of them are at the pumping station on the In Woodridge, at Twenty-fourth and Irving Streets, low plain near the eastern edge of Bollirg Field, and nearly a mile north of Langdon, a 312-foot hole bored the third is on the high terrace a mile east of the about 1903 reported "rock" under Potomac clay and hospital. sand at 167 feet below sea level. This figure falls in a plane with the slope indicated by supposed bedrock con 15 See also table, page 38. PRINCE GEORGES COUNTY, MD. 29 The 590-foot hole was bored in 1907. The record about 1934, and by several test borings made to ascer supplied by the drillers is given below. The fine gray tain foundation conditions. The following record of arkosic sand reported at a depth of 400 feet is probably the well was furnished by the drillers: bedrock, for it was classed as "Piedmont crystalline" in Well at gas tawJcs on Chillum Road the log, and hard rock began at 440 feet. The sedi Feet mentary material is all of Potomac age, and the very Soil on muck______-_———__ 0-10 coarse gravel extending from 350 to 379 feet is basal Clay, very compact, white—————————————————— 10-18 Sand ______———_ 18-36 Potomac, Clay, yellow above, blue below_—————————————— 36-45 As this hole is on the lowland about 120 feet below Rock, rotten______———— 45-68 the contact between the Potomac group and the Mag- Rock, hard______—————_————— 68 othy formation in the terrace to the east, the record In the test borings rock was mostly reported as hard indicates that the deposits of Potomac age lying on bed greenish clay, and it was noted that its surface sloped rock are here about 560 feet thick. The records accord to the east. Considerable lignite was found in the in indicating the altitude of the bedrock surface at about sands and clays of the Potomac group. 390 feet below sea level. HYATTSVILLE 590-foot well at St. Elizabeths Hospital Feet Several holes in or near Hyattsville have reached bed Sand and clay______0-40 rock or ended in the immediately overlying sand and Clay, reddish yellow on red______40-60 gravel (Potomac). One on the Lewin place (prior to Clay, blue, few pebbles—-______60-70 Clay, sandy, reddish brown______70-120 1915), a short distance west of the railroad station, Clay, dark gray; some sand, pebbles and iron concre ended in coarse sand at a depth of 206 feet; othe^ at tions ______120-130 the Waterworks (1908) at 242 feet, and one at th<* ice Sandstone, brown______130-150 works, 285 feet deep, ended in sand. A well a quarter of Sand, gray or brownish; pebbly______150-170 a mile east of the village, on the low flat, reported gran Clay, sandy, gray——______170-180 Sand, pebbly, light brown______180-190 ite at 247 feet, and a well at the Hot Shoppe (A. & W.), Clay, sandy, light gray______190-210 5315 Baltimore Avenue, sunk in 1940, has the following Sand, coarse, light gray______210-214 record: Clay, sandy, brownish gray on reddish brown_____ 214-230 Well at Hot Shoppe (A. & Tfl), Hyattsville Clay, pink on brown______230-250 Feet Clay, sandy, bluish gray on brown______250-270 Clay (brown), sandy above, blue below————————— 0-68 Sand, light brown______270-280 Sand, fine______———_———— 6" -92 Clay, sandy, gray———_———______280-300 Clay, blue, with red clay at 120-145 feet______,. 9

AGRICULTURAL RESEARCH CENTER, BELTSVILLE Feet Sand, gray, medium coarse———————————————— 935-945 Bedrock was reached by most of the holes bored at the Bedrock, weathered rust-colored; fragments of quartz, Agricultural Research Center of the United States De feldspar, and hornblende_——————————————— At 946 partment of Agriculture east of Beltsville, Md. The This hole is located on the slope of a slight depression principal data reported are given in the table on page 38, a few rods east of the main building and near the top of and locations of the holes are shown on plate 1. The the Potomac strata. The rate of slope of the bedrock records are fairly satisfactory and accordant and indi surface indicated is close to 110 feet to the mile, when cate that the regular slope of about 100 feet to the mile compared with holes at the Beltsville experimental continues eastward to 100 feet below sea level, where farm and a hole at Muirkirk where the bedrock surface locally the rate diminishes somewhat. The F. D. well is 22 feet above sea level. The general structure is 1, in which rock was reported at a depth of 260 feet, shown by the section in figure 3. indicates the presence of an underground mound, for in hole Al. No. 2 the rock was found at a depth of 315 MEADOWS feet, and in hole N at 307 feet below the surface, indi In 1902 a hole was bored by Capt. F. A. Lucas at a cating a valley in the bedrock surface. point about half a mile south of Meadows (Centerville), GLENN DALE later a part of the farm of L. C. Matthews. It was started at an altitude of 260 feet and ended at a depth of Three test holes were drilled at the Glenn Dale Sana 1,511 feet in a thick body of dark-colored clay with some torium, 3 miles due east of Lanham (outside the area sand and gravel, doubtless the lower beds of the Poto shown on pi. 1), two of them to bedrock. The first one, mac group.18 More than a thousand feet of the Po drilled in May 1936, reached rock at 950 feet; hole 3, tomac group was penetrated. A short time later Champ drilled in 1938, reached rock at 946 feet. As these holes Eobinson, of Baltimore, bored in the vicinity a hole were at an altitude of about 145 feet, the bedrock sur that is reported to have reached a depth of 1,728 feet, face here is close to 800 feet below sea level. The fol or an altitude of about 1,468 feet below sea level. Mr. lowing record is condensed from notes by F. H. Klaer. Robinson stated the depth to Arthur Bibbins, who is Well 3 at Glenn Dale Sanatorium authority for the report that the hole ended in reddish- Clay, red and white and reddish brown, sandy near Feet brown sandy clay. The distance to bedrock here is base______0-234 not known, but the depth of the hole indicates an in Sand, reddish brown, some reddish clay______234-244 crease in the rate of declivity of the bedrock surface Clay, blocky with nodules and few pebbles______244-254 greater than that suggested by holes farther west. Clay, red, brown and gray; red, sandy in lower part_ 254-300 Sand, pinkish white, moderately fine, some clay below; PORESTVILLE water 300-310 feet______300-317 A hole was bored by the Potomac Oil & Gas Co. in Sandy clay, white______317-319 Sand, clean, white above pink, some coarse and fine the late spring of 1920 at a point about four-fifths of a gravel at base______319-340 mile west of Forestville, at an altitude of 280 feet. The Sand and clay, pink, intermixed, few small pebbles__ 340-349 depth of this hole is not on record, but a notation on a Clay, sandy, white and red______349-354 reference card in the United States Geological Survey Sand, reddish, grades down into coarse sand and files gives 1,400 feet as its total depth, and a letter to me red sand and gravel______-______354-373 Clay, brick-red, dark gray, tough in center______373-414 from Arthur Bibbins, geologist of the company, stated Sandy clay, red brown and white, some small pebbles— 414-424 that he was informed that it reached gra.nite "about Sand, reddish, grades down into coarse sand and the depth expected on the basis of the average bed gravel; water, 450-460 feet______424-474 rock slope elsewhere of about 60 feet per mile." It is Clay, blocky, some gravel, grading down into red and stated that the oil company sank another hole in the gray clay—______474-494 Clay, yellowish brown sandy and tough, brick red__ 494-540 same general vicinity, but no data were oHained. Clay, brown to buff on purplish and brick red_____ 540-620 FORT WASHINGTON Clay, tough, red on yellowish______^___ 620-670 Sandy clay, pink and white with ironstone layers___ 670-700 A 1,000-foot hole at Fort Washington failed to reach Sand, coarse and gravelly near bottom; water 726-732 bedrock. This hole began near the top of the Potomac feet ______700-734 group and ended in clays of that group. Bedrock prob Clay, sandy, coarse, gray______734-745 ably is not far below, or near 900 feet belcw sea level. Sand and gravel, coarse at base; water, 750-753 feet_ 745-753 Sand, fine, dirty, some clay near base______753-767 The subsurface relations between the Fort Washington Sand, red, and gravel on gray sandy, gravelly clay___ 767-785 area and the area on the Virginia side of the Potomac Clay, brick red, brown and gray, on white and gray__ 785-854 River are indicated in figure 27, section A, r,nd a record Sand and gravel on dirty gray sand. Water 854 to of the lower part of the Fort Washington 1 ole is given 856 feet——______854-864 on page 31. Clay, gray and pink brown—_——______864-884 Sand, light brown and gray______884-910 18 A log of this well by N. H. Darton is given in Maryland Geol. Survey Clay, dark gray, tough______At 920 Report, vol. 10, pp. 383-384, 1918. ARLINGTON COUNTY, VA. 31

Partial record of a deep boring at Fort Washington, Md. at the Norton rendering plant reached it at about 95 Feet feet. A 102-foot hole bored in 1925 by Mr. Hagman at Clay, blue______582%-584% a transient amusement park at the former Hoove^ Air Sandstone, soft gray______584^-600 port (then on Alexander Island), entered bedrock be Clay, yellow on blue______600-627 Clay, blue, with sand______627-677 tween 90 and 92 feet below the surface. A hole bored Clay, yellow______677-718 to a depth of 330 feet in the Hoover Airport by Mr. "Rock," with 2 feet of yellow clay______718-726^ Dowling in 1926 penetrated schist, but no datr, were Clay, blue, with sand______726V2-732i/2 obtained as to the position of the top of the rock. Sand, fine, white______732%-737% Clay, light red, with sand______737^-765^. Samples of "gray sand" submitted to the Geological Gravel, coarse——______765^-785^ Survey as coming "from above 320 feet" in this hole "Slate" ______785%-790 contained rounded grains that were evidently of sedi Sand, some yellow clay______790-846 mentary origin, but they probably came from high up. Clay, yellow and blue, some sand near base____ 846-1,000 The hole was shot when its depth was between 320 and CHARLES COUNTY 330 feet and yielded masses of schist from an ur stated INDIAN HEAD depth in its wall, presumably near 325 feet. It is stated that the rate of drilling changed from 20 to 3 ff°,t per A boring at the Naval Proving Grounds, Indian day at 320 feet in this hole, which, if it is a fact, would Head, in Charles County, is reported to have entered give the impression that the top of bedrock was entered rock at a depth of 735 feet. A blueprint of the log gives at that depth. However the evidence of other holes no data for a gap of 32 feet between a thick body of in the vicinity is that the top of bedrock is her"* only clay extending to a depth of 708 feet and the "hard 100 feet below sea level, as shown on the map in the rock" from 740 to 1,200 feet. Another statement is that Washington folio.20 Any local trough or deep reentrant the "last 450 feet, at least, were in solid rock." The in the otherwise regular slope at this place is most elevation of the hole is about 95 feet above sea level. unlikely. The slope of the bedrock surface is shown in figure 27, The Morris No. 2 well in Aurora Hills near Oakcrest, section G. 538 feet deep, and at an altitude of about 150 feet, pene VIRGINIA 19 trated bedrock, but no information was given as to the ARLINGTON COUNTY depth to its top. In many places the decayed upper The floor of granite gneiss and other crystalline rocks portion of the gneiss or schist is so completely disinte rises above sea level near the center of Arlington County grated that it is regarded as sand by the driller, ar d this and attains an altitude of nearly 450 feet at Minor Hill, was doubtless true at this place. on the west line of the county. The basal or marginal PENTAGON BUILDING gravels of the Potomac group rise to an altitude of In 1941 two sites were under consideration for an office about 350 feet west of Clarendon, and they occur as building in Virginia for the War Department. Both outliers on some of the slopes to the west. They are were on low terraces between the Potomac River and deeply trenched by the valleys of Fourmile Run and Arlington Ridge Road, the Arlington Memorial High Potomac River, down which the outcrops of gneiss ex way, and U. S. Highway No. 1. The first site was in tend for several miles. In the sides of these valleys the the northern part of the experimental farm of tl n De contact of gravel on bedrock slopes at the rate of about partment of Agriculture; the second, finally seated 100 feet to the mile east-southeast, and although there for building, was partly on the former Hoover Airport. are some local variations of rate and direction of slope Both sites were explored as to underground conditions no marked irregularities of configuration are apparent. by holes, mostly from 30 to 60 feet deep, bored at corners Borings on the plateaus and terraces from Clarendon of squares 200 feet on a side in a checkerboard arrange to Alexandria afford data for the underground con ment about 30° out of meridional alinement. Th^. pur tours in that area. pose was to reach "bedrock" or "refusal" for piles, and It was stated years ago that a boring for an abutment although some of the materials penetrated were not dis of the old Long Bridge reached "rock" at a depth not far criminated accurately, the records of the holes throw below 100 feet. This was verified by the 314-foot hole much light on the geology and configuration of th e bed at the American Oil Co. filling station one-half mile rock surface. The location of the holes and some of the southwest of Highway Bridge where "bedrock" was reported results of the boring are shown in figure 26, entered at a depth of 114 feet, and by the McGuire and constructed from drillers' records furnished by F. W. Rolfe hole, 303^ feet deep, a few rods southwest, which Walker, constructing architect of the Quartermaster reported "bedrock" at a depth of 105 feet and contains Department. The materials penetrated were pumped 112 feet of 6-inch casing. At the oxygen factory nearby out as a casing was sunk, and most of the holes r.re re- a boring 97 feet deep did not reach bedrock, but a hole 20 Barton, N. H., and Keith, Arthur, U. S. Geol. Survey Geol Atlas 19 See also table, page 39. Washington, D. C.-Md.-Va. folio (No. 70), 1901. 32 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA

EXPLANATION • Borehole.showing oltitude of bednck surface

Borehole, showing altitude of bedrock or hard layer reported as bedrock

Borehole, showing oltitude of herd layer reported as bedrock

Borehole, ending in sand, grave'. or clay

— •— — —— -35— —— Contours on surface of roc'- or some other hard materia1

U S. Army Engineers datim

FIGURE 26.—Map of eastern part of Arlington County, Va., showing boreholes in site of Pentagon Building and adjacent area. FAIRFAX COUNTY, VA. 33 ported to have stopped at "rock" or "boulder". In some Hole 5 (east) peet holes the rock reported may not have been true bedrock. Water ______0-28 In 40 holes "mica schist" or "crushed rock" was re Mud, some sand below______——_ 28-81 ported for a few feet. Sand, medium______81-86 Sand, hard, and clay______86-126 The edge of the Potomac group is known to be about Clay, hard, sandy______126-157 100 feet below sea level in several old holes along or near Clay, hard—______157-169 Highway No. 1 and at less depth, rising to the west, Clay and sand______169-201 along Columbia Pike. A considerable part, if not all FAIRFAX COUNTY 22 of the area shown in figure 26, is in an old trench of the Potomac Eiver, cut nearly 100 feet deep in places The bedrock floor of gneiss and other crystallite rocks through the eastward-sloping Potomac group into the rises gradually from below sea level in the eastern part underlying bedrock. All of it is floored by river de of Fairfax County and appears in ledges in the larger posits. The configuration of the rock surface or floor valleys about 5 miles west of the Potomac Hirer. It under the river deposits is not known in detail, but has been reached by various wells, and these an d some the boreholes show that it is of irregular contour, with deep borings ending in Potomac deposits indicate the valleys and ridges of considerable size. Some features general configuration of the floor in the area where it of this configuration are shown approximately in figure is buried. The deeper contour lines in plate 1 a re con 26 by underground contour lines drawn on the assump structed from these data, and those from +100 feet to tion that "rock" or "refusal" in the borehole records +250 feet are in greater part based on contacts of gneiss indicates bedrock surface. and basal Potomac deposits exposed along the rides of One 26-foot hole at an altitude of 39 feet 400 feet the intervening ridges. The relations indicate a re west of the northern point of the Pentagon Building markably regular slope of about 100 feet to tte mile, had a rather doubtful report of mica schist at the bot and probably there are but few local variations in this tom at +13 feet, under brown clay, sand, and gravel. rate or few notable old topographic features buried Possibly there is here a local high place in the floor, under the Potomac deposits. This is in accord with and other holes near and under the southern and west observations in the outcrop zone in Maryland already ern parts of the building, which were sunk to only a described, and it indicates that, in general thn base few feet above sea level, may indicate the presence of ment is a nearly smooth plain sloping east-soutKast at an underground mound of considerable extent and a fairly regular rate. prominence. SEMINARY RIDGE ALEXANDRIA a Two deep borings made in Alexandria many years The borings on "Seminary Bidge" from Seminary ago at the ice plant and the brewery undoubtedly failed Station to the vicinity of School A, indicate some local to reach bedrock, the depth of which under Alexandria irregularity in the configuration of the bedrock furface. is not known precisely. Near the wharves it is about A 150-foot well a quarter of a mile southeast, of the 500 feet. Theological Seminary, at an altitude of 200 feet, found AUEXANDRIA TUNNEL (PROPOSED 1941) no rock. A series of holes was bored from Alexandria, Va., A hole just north of old Fort Crawford, half a mile across Potomac Kiver to Marbury Point, D. C., by the north of Seminary Station, at an altitude of 230 feet, Corps of Engineers, United States Army, for the office had 240 feet of casing, all in the Potomac group, indi of the Quartermaster General. Records of the two cating that the bedrock surface at that place is lower deepest holes in the bottom of the river area follow. At than 10 feet below sea level. this place bedrock was to be expected at a depth of The 448-foot hole at the Episcopal High School, at about 500 feet. The clay and sand penetrated under an altitude of 260 feet, reported granite from 440 to the mud is part of the Potomac group. 448 feet, but no log seems to be available and no data Hole 4 (west) Peet as to the top of the granite, which I believe mu?t have Water (mean low tide)______0-29 been entered at a depth of about 300 feet, or al^ut 40 Mud, mostly soft______29-58 feet below sea level. Another hole at the same altitude Mud, some sand, stiff below______58-65 and 300 feet deep reported "petrified wood" at the Sand, some mud, mixed______65-74 Sand, medium______74-84 bottom. Sand, fine, and clay, soft______84-124 A 170-foot well a third of a mile north-northwest of Clay, hard to medium______124-152 the Episcopal High School and at about the sane alti Clay, sandy.______152-162 tude penetrated granite from 165 to 170 feet, indicating Sand, coarse, some clay______162-182 Clay, hard______182-201 that the surface of bedrock is 95 feet above sea le^el. A 21 See also table, page 39. 22 See also table, page 39. 34 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA 205-foot well at a house a third of a mile northwest FORT BELVOIR of the Episcopal High School, at an altitude of 272 feet, In a test hole at Accotink for Fort Belvoir (formerly contains 192 feet of casing extending to an altitude of Fort Humphrey), "hard rock" was penetrated from about 80 feet above sea level, probably nearly to depths of 253 to 272 feet and gneiss from depths of bedrock. 272 to 279 feet. (See fig. 27, B.) It is evident from the above data that there is a zone MOUNT VERNON of steep slope in the bedrock surface near the Episcopal High School, northwest of Alexandria. Probably At Mount Vernon, a hole at the tool shed, about 100 when more data are available it will be found that there feet above sea level, is in water-bearing sard from 522 are various other local irregularities of this kind in to 530 feet. A hole at the edge of the Potomac River the bedrock floor. nearby penetrated bedrock from 515 to 525 feet, begin ning at about 515 feet below sea level, as shown in FORT HUNT figure 27, B. Several deep borings throw light on the configuration of the buried bedrock surface in the southern part of DATA ON BOREHOLES AND EXCAVATONS Fairfax County. Data supplied by D. J. Cederstrom, INDICATING ALTITUDE OF BEDROCK of the Geological Survey, have aided in locating bed The table that follows lists the boreholes described rock contour lines along the south edge of the map (pi. in the text and some other holes and excavations for 1). The available information indicates remarkable which information was available. The localities are regularity in the rate and direction of slope of the bed arranged first by numbered streets, in order from lowest rock surface, as shown in the three cross sections in to highest, then by lettered streets. Avenue? have been figure 27. fitted in between the adjacent numbered and lettered A 284-foot hole at Fort Hunt is reported to have streets. Constitution Avenue and Independence Ave reached bedrock, but considering the general relations nue are equivalent to B Street north and south. For the shown in figure 27, A, and the fact that a 1,000-foot localities in Maryland and Virginia a similar arrange hole at Fort Washington, Md., failed to reach bedrock ment in north-south or east-west has been followed as (see p. 31), the report is believed to be a mistake. far as practicable.

RAILROAD Terrace gravel Fort Hunt Fort Washington Sea teve/_ -\<^v?r7y- — ^ " •"••*••=• " sSri D°Sue Creak Terrace deposit on Potomac group Porow/5cxiT- , — r-—*i •"•v-f'-*i*-*^ x - / _v - ^^ Gneiss ,~) ^-\ •'~\~^-j-r- 7 _ __ 7 .... Monmouth U-240 formation ~ ' ~ x~" \ X J'""'' C.'^^-^^^" — — — _ Potomac group Bedrock ' ^ ' v 'v~x 'O~ ~ ~

'''\ Gneiss ,^7^ -1000' -860'

w. R.F. AND P. RAILROAD Pohick Station

Gravel T^r>-r->YJ1»^ff-^g~-'-^--~ ,,- .. elmont Bay ,,,. t __ San^i_KS^l___ POTOMAG RIVER^c,a-t.„?,'.*• _Miocene

Bedrock ' " /v "• ''\~) '1000'-

2 Miles FIGURE 27.—Sections from southern Fairfax County, Va., eastward into Maryland. A, Through Fort Hunt, Va., and Fort Washington, Md. B, From Pohick Station, Va., through Mount Vernon to Accokeek, Md.; G, From Woodbridge, Va., through Indian Head, Md. DATA ON BOREHOLES AND EXCAVATIONS 35

Data on boreholes and excavations, indicating altitude of bedrock

Depth of Land surface Bedrock surface Location hole altitude Materials altitude (feet) vfeet) (feet)

District of Colombia NORTHWEST WASHINGTON [See also pages 8-20. ]

1140 North Capitol St. (near M St.; Sibley 161 50 Rotten rock at 154 feet. -104 Memorial Hospital). 52 G St. (between North Capitol and 1st Sts.; 130 27 Rock at 105-130 feet_ -78 old location of Yale Laundry). 1st and G Sts. (old Gales School) ______141 30 Soft rock (gneiss) at 133-141 feet, under -103 water sand. 1620 1st St. (near R St. and Florida Ave.) _ _ _ 122 72 Rotten rock at 118-122 feet, under sand___ -46 3d and H Sts._._.____...______166). 48 Soft rock at 158 feet, under blue clay___-_ -110 4th St. and Pennsylvania Ave. (proposed 179 20 Rotten rock at 174 feet, under gravel, etc_ -154 Municipal Center). 460 K St.1-...-______--_-_-_-__-______100 80 No record______--____-__-._-_-. 4th and 5th Sts., N St. between______150 82 Talcose rock at 127-144 feet under sandy -45 muck. 5th and L Sts.1 -....____.______. 120 60 No record___.______.______-___-__-. Belov —60 5th and Tuckerman Sts. (Calvin Coolidge 11-40 247 Footings on rock_-______-___--__-_---. 211 to 230 High School). 6th and B Sts. (old pump)______140 8 Soft rock at 125-134 feet, hard 134-140 feet. -117 6th and 7th Sts., Constitution and Pennsyl 70 5-10 Clay 15-25 feet, clay and sand 50-60 feet- _. Below —115 vania Aves. (Apex Building; Federal Trade Commission; 6 holes).1 6th and 7th Sts., O St. between_____.____. 201 Soapstone and gneiss 100-201 feet. -14 7th St. north of B St. (old Center Market)_. 628 8 Rock at 120 feet__-.___-_____. -112 434 7th St. (between D and E; S. S. Kresge 90 30 No record.______Co.) i 7th and M Sts.1___.______. 151 87 "Conglomerate" 143-151 feet, possibly on Below —64 bedrock. 721 MSt-__-_-___--__-__-_- 120 82 Gneiss at 98 feet__-__-__-___-----_-----. -16 2146 Georgia Ave. (near V St.). 500 100 "Medium hard rock" at 79 feet, under sand 21 and gravel, soiid rock at 89 feet. Another report gave blue clay and gravel to 87 feet, where "solid rock" was entered. 7th and 9th Sts., Constitution and Pennsyl 65-120 5-10 Fill, river deposits, sand, and clay to bed -74 to-103 vania Aves. (National Archives; 19 holes). rock. Some thin gravel beds. 8th St. and Florida Ave. (near U St.)______. 103 "Granite and soapstone" at 60 feet______8th St. between Upshur and Varnum Sts.1__, 195). 200 Soft rock at 75 feet, under gravel_-______. 125 Qth'and D Sts. (U. S. test hole)______. 95 12 Bedrock at bottom, under arkose 55-95 feet. -83 425 9th St. (between D and E; Central Thea 127). 30 No record______Below — 97J4 ter).1 9th St. and New York Ave. SW corner.______183 55 Rock at 133 feet, under sand and clay. -78 909 Pennsylvania Ave.1 .------.--....--.-. 81 12 No record. 411 10th St. (between D and E; old building of 77 25 Clay with some sand and gravel. Ends in Below -52 Washington Gas Light Co.) 1 very dark clay. 10th and E Sts______-______.__. 116 30 Test hole; rock at 94-116 feet______. -64 10th and 12th Sts., Constitution Ave. and C St. 68-83 5-10 Mud, sand, clay, and gravel on mica schist.. -60 to -65 (Internal Revenue Bureau; 9 holes). llth St. and Pennsylvania Ave. SE corner 60 12 Clay and sand.______(near D St.; old Harvey's Restaurant).1 11th and E Sts. (Harrington Hotel, basement). 83 15 Clay, sand, and gravel. Below —68 llth and G Sts., NE. corner (Woodward & 97 37 Ended in gravel Below -60 Lothrop North Building, formerly Palais Royal). llth and G Sts., NW. corner (S. S. Kresge 85 37 No record. Co.).1 2012 llth St. (between U and V Sts.; Thomp 80 95 No record. 15 son's Dairy). 1110 New York Ave. (Greyhound Lines) 1__. 124 55 Sand and graveL______-_-_-----_---__. Below —70 12th St. and Constitution Ave. (Interstate 60-80 7-10 Fill, clay, silt, sand, and gravel on rock___. -54 to -69 Commerce Commission; 13 holes). 12th and F Sts., NW corner (F. W. Wool- 88 35 Clay, sand, etc-______--__------. Below —53 worth Co. ).* 1214 G St. (G. C. Murphy Co.)______.______103 37 Rotten rock at 102 feet.______-65 12th and M Sts. (Security Storage Co.)___.__. 149 87 Soft rock at 102-115 feet, hard talc rock at -15 115-149 feet. 12th and V Sts______._____.______. 135 100 Rotten rock at 44 feet.______56 12th and 13th Sts., Pennsylvania Ave. between 70-80 8-11 Bedrock.______-65 (Post Office Department; many holes). 725 13th St. (between G and H; Chesapeake 125 40 Rock at 122-125 feet, under 30 feet of clay_. -82 & Potomac Telephone Co.). 14th St. and Constitution Avenue (Labor 68-80 7-12 Fill, clay, silt, sand, and gravel on rock___. -55 tc -68 Department; 12 holes). 14th and D Sts. (old electric power plant) 1_. 78 10 No record______14th and D Sts. (U. S. test hole) »______. Bedrock______---_-_-_------. 14th and F Sts. (Julius Garfinckel & Co., sub- 69 35 Ended in black mud____-______- Below —34 basement).1 1 Not on plate 1. 36 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA.

Data on "boreholes and excavations, indicating altitude of bedrock—Continued

Depth of Bedrock surface Location hole Materials altitude (feet) (feet)

NORTHWEST WASHINGTON—Continued

14th and K Sts., SW. corner (Ambassador 102 62 Rotten rock at 96 feet, hard at 101 feet- -34 Hotel). 14th and K Sts., NE. corner (Hamilton Hotel, 85 42 Rotten rock at 77 feet, under gravel, hard -35 basement) .1 rock at 85 feet. 14th and R Sts. (Chesapeake & Potomac Tele 110 101 Soft rock at 98feet, under gravel.______3 phone Co.). 3128 14th St. (near Irving St.; G. C. Murphy 102 192 Rotten rock at 82-102 feet, under clay, sanc\ 110? Co.). and gravel. 14th and 15th Sts., E St. and Constitution Ave. 77-90 8-15 Bedrock at 66 to 87 feet.______-58 to -74 (Commerce Department; 18holes). 15th St. between Pennsylvania Avenue and 140 30 Rotten rock at 120 feet, hard at 140 feet___ -90 F St. (old Corcoran Building; present site of Washington Hotel). 15th and G Sts., SE. corner (Keith's Theater; 558 "Schist" under terrace deposits. site of old Riggs House). 15th andH Sts. (Shoreham Building)______110 60 "Gravel on crystalline rock"______. -48 15th and M Sts. (Security Storage Co.) ______99 70 To rock. Another report records rock at -29 46 feet (altitude +24 feet). 715 Madison Place (between Pennsylvania 70 51 Ends in clay______-__--______-_------Below —19 Ave. and H St: east of Lafayette Square; old Belasco Theater). 1619 Q St. (Cairo Hotel)______.______312 85 0-70 feet clay, 70-312 feet granite______15 17th St. between Pennsylvania Ave. and H 60-65 55-67 4 holes to rock; each penetrated rock 10 feet_. -10 to -5.7 St. (square 167, west half; 6 holes).1 17th St. and Connecticut Ave., L and DeSales 40 57 Excavation through Potomac group_____. 19 to 21 Sts. (Mayflower Hotel). 17th and 18th, D and E Sts. (American Na 45-75 23-35 15 holes to rock, under terrace deposit- -23 to -39 tional Red Cross; 15 holes). Champlain St. and Florida Ave. NE. corner 5 115 Pit through arkose to granite______110 (between 17th and 18th Sts. near V St.). 1 18th St. and Constitution Ave. (Navy De 30-48 About 15 Fill, sand, peat and some gravel on rock_. -18 to -33 partment; 17 holes). 18th St. between California St. and Wyoming 10 135 Fault; gneiss on west, arkose of Potomac 135 Ave.1 group on east. 18th and 19th, C and E Sts. (Interior De partment) : 18th and D Sts______. 59 27 Test holes to gneiss.______-32 18th and E Sts______. 67 35 .-32 18th to 19th Sts. near C St______. 53 22 _do. -31 18th to 19th Sts. near E St.______62 37 _do- -25 19th and D Sts_.______. 57 31 . do- -26 19th and 20th Sts., Constitution Ave. and C 55-60 About 22 Fill 25 to 30 feet; clay, sand, and gravel or -25 to -32 St. (square 128; 8 holes).1 gneiss. 20th and B Sts. (U S. test hole).1....____. No record______-----_-_--___--. -25 20th St. and Pennsylvania Ave______203^ 72 Rock at 43 feet, under terrace gravel.___. 29 20th and M Sts. (brewery).i______. 900 """"25-32" All gneiss below terrace deposit.______20th and 21st St., Constitution Ave. and C St. 42-58 Fill, mud, clay, sand, and boulders.__-__-. — 9 to -24 (Federal Reserve Board; 12 holes).1 20th and 21st, C and D Sts. (21 holes)--___. 34-77 25-40 Fill, clay, silt, sand, and gravel______— 3 to —25 2107 Pennsylvania Ave. (bet. I and K).1 -..... 12 About 70 Decayed rock under terrace gravel______. 60 21st and M Sts.1 .______.. 150 60 Gravel at 5-25 feet, soft rock 25-33 feet, 25 hard rock 33 feet to bottom. 21st and 22d Sts., Constitution Ave. and C St. 35-40? About 30 Fill 5 to 10 feet thick, clay and sand 6 to 28 12 to —8 (National Academy of Sciences; 4 holes). feet thick, on decomposed rock. 21st and 22d, C and D.Sts., at Virginia Ave. 10-70 30-60 Fill, clay, sand, and gravel on rock______20 to -24 (State Department; 55 bore holes). 21st and 22d Sts., E St. between.1______132 65 All gneiss below terrace deposit. Lydecker Tunnel shafts: East end, at McMillan Reservoir. ______Chloritic gneiss at 102-148}. feet___. 29/2 13th St. north of Florida Ave______125 140 Talcose schist at 80 feet______60 Another record gives rock at 96 feet. 44 Soldiers' Home: Pump ______205 209 Soft rock at 173 feet, under green clay__- 35 Pump house______-__-____-___--_-. 478 209 Rock at 174-478 feet, under gravel-_____ 35 Brightwood, Georgia Ave. near Peabody St__. 146 291 Soft rock at 64 feet, "gneiss" 99-146 feet- 227

SOUTHWEST WASHINGTON [See also pages 20-27]

Half St. (between South Capitol 207Y2 22.4 Below -185 at T St. 2d St. at E St. and Virginia Ave 146 12 Below -134 324 B St______147 11 Below -136 3d and D Sts.1 ______. 06 13 Below -83 4th and B Sts. (formerly 4)4 and B Sts.)______141 11 Below -130 1 Not on plate 1. DATA ON BOREHOLES AND EXCAVATIONS 37

Data on boreholes and excavations, indicating altitude of bedrock—Continued

Depth of Land surface Bedrock surface Location hole altitude Materials altitrde (feet) (feet) (fee*,)

SOUTHWEST •WASHINGTON—Continued

4th and O Sts. (formerly 4& and O Sts.; old 208 12 Sand at 198-208 feet ______Below -196 powerhouse). 6th and G Sts. (SE. corner)....- __ _ _ ... 145 24VS Clay and sand _ _ _ _ _ .______Below -120 623 D St. (or 630 Virginia Ave.; formerly 202 28 Rotten rock at bottom. ______At -174 Auth's).1 7th and H Sts ______144 22 Clay and sand______Below —122 12th and C Sts. (Agriculture Department) ____ 90 37 Blue rock at 89-90 feet, under 5 feet of blue -At -53 clay, which is overlain by sand, gravel, and clay. 14th and D Sts______. ______247 25 Rock, soft 110-144 feet, hard 144-247 feet_. At -85 Washington Monument (15th and 16th Sts., 72-128 10-40 Fill, sand, gravel, and river silt to bedrock __ From —55 Independence and Constitution Avenues; to -71 15 holes). Jefferson Memorial (Tidal Basin; 27 test holes) _ 60-150 8-10 Fill, river silt, sand, and gravel to bedrock. _ From —65 to -91 Reflecting Pool (between 17th and 22d Sts., 27-50 About 10 Clay and sand ______From -17 Independence and Constitution Avenues; to -40. 11 holes). Lincoln Memorial (23d St. between Constitu 42-56 16 From —28 tion and Independence Avenues; 20 test to —40. holes) . Ericsson Memorial (23d St. and Riverside 53 12 At -41 Drive) . Water Gate (west of Lincoln Memorial at edge 15-58 6-20 From —20 of Potomac River; 69 holes). to -42. Arlington Memorial Bridge (many jet prob- 50-70 From —35 ings; 23 core borings). low water to -50. to 10. Highway Bridge (8 holes) ______Mud, sand, gravel, and clay to bedrock. From —84 low water. to -110. Railroad Bridge, hole 2______-30 Gravel, sand, and clay to bedrock _ _ _ _ _ -102

NORTHEAST WASHINGTON [See also pages 27-28]

North Capitol and G Sts. (old Pabst Brewery).1. 96 26 Sand and graveL ______Below — 70 60 M St. (Southern Dairies) »_.______176 60 Below —116 18 O St. (Goldcraft Co.) ______159 58 Rock, 158-159 feet under sand and clay __ -100 Lincoln Road and S St. (east of North Capitol 162 110 -38 St.).- Washington Terminal Co.: 1st and K Sts_____-______210 50 Bedrock, 170-210 feet. ______-120 3d St. and Florida Ave ______185 60 Below - 125 New York Ave. at Fairview Ave______175 Q^ 300 feet east of round house______218 Q^ do - _ Below - 123 260 98 ___-_do___. _ _-___--_--__-_-_-____-___- Below -162 New York Ave. at Montana Ave______260 95 _____do____-______--______Below -165 1st and Patterson Sts. (between M and N Sts.; 210 47 Granite, 197-210 feet __. ______-150 Chapin-Sacks Corp.).1 Do______.______208 42 Hard rock, 145-208 feet _. ______-103 SdandHSts ______157 44# Below -112 3d St. and Florida Ave ______185 68 Below -117 4th and C Sts. and Maryland Ave. (Stanton 232 80 Clays and sands, clay 81-197 feet- _ Below —152 Square) . 4th and F Sts. (old brewery) ______300 45 Water at 270 feet ______... ______Below —255 4th and R Sts. (old powerhouse) ______225 80 Bedrock, 159-225 feet under gravel . ___ -79 4th and 5th Sts., U St. Between. _ _ __ _ 150 84 -43 1262 5th St. (between M and N).___. ______162 79 Dark gray tough clay, 150-162 feet. _ Belovr -83 7th St. between A and B Sts. (Chesapeake & 331 67 Rock, 328-331 feet.. . ___ .______-261 Potomac Telephone Co.). 7th and D Sts. and Maryland Ave______232 75 Water sand 218-232 feet- ______Below - 157 llth and East Capitol Sts. (Lincoln Park, 181 85 Clay 33-178 feet, sand 178-181 feet ___ __ Beloy —96 SW corner). 12th and K Sts. ______188 45 Below — 143 Warren and B Sts. (between 14th St. and 125 80 Red clay, 52-120 feet, sand 120-124 feet___ Belovr —45 Tennessee Ave.).1 1400 Rhode Island Ave. (between Evarts and 298 171 Rotten rock under water-sand at 284 feet- -123 Franklin Sts.; Hot Shoppe). 15th and E Sts. (old Hygienic Ice Works) _ _ 365 en Bedrock, 350-365 feet— ----- ______-300 1Q7 45 Clays and sands, sand 186-196 under red Below - 152 clay. 911 Bladensburg Road (between 16th and 17th, 304 54 Stopped in gravel —— ______Below —250 Neal and K Sts.; Sears, Roebuck & Co.). 2301 Bladensburg Road (between Queens 139^ 50 Chapel Road and 24th Place; Hot Shoppe).1 1 Not on plate 1. 38 BEDROCK SURFACE OF THE DISTRICT OF COLUMBIA

Data on boreholes and excavations, indicating altitude of bedrock—Continued

Depth of Land surface Bedrock surface Location hole altitude Materials altitude (feet) (feet) (feet)

NORTHEAST WASHINGTON—Continued

260 60 Above - 190 24th to 26th Sts., south of Douglas St. (Lang- 207 60 don; Standard Brands Inc.). 247 60 "Reached rock" at 244 feet__.______-184 Do_ _ 262 60 "Boulders" at 260-262 feet, on rock. _ _ _ -200 Do 220 55 Rock 217-220 feet— ______-162 24th and Irving Sts. (Woodridge) _ _ _ _ 312 145 "Stopped at rock under 8 feet of sand". __ -167 183 180 270 170 Below -100 burg Road and South Dakota Ave.).

SOUTHEAST WASHINGTON [See aUo pages 28-29]

South Capitol and E Sts. (Colonial Ice Cream 273 10 Bedrock 247-273 feet ______-237 Co.). 41 L St. (Wakefield Dairy) ______120 30 Below —90 Naval Gun Factory (between 1st and llth Sts., 162K 20 Clay and sand... ______Below - 142 M St. and Ancostia River).1 2d and D Sts. and North Carolina Ave______232^ 67 Blue clay, mostly, to 232 feet— — — .- — Below —166 3d and M Sts______223 15 Below -208 10th St. and South Carolina Ave.1-- _ _ _-_ 147 77 Clay and sand, coarse sand at bottom. _ _ _ Below —70 12th St. and Virginia Ave ______290 49 Below —241 1337 D St. (Carry Ice Cream Co.) !______300 76 Below -224 Do— ______325 76 __ -do__ „ ______Below -249 14th and C Sts.i______. .__.-._.. 149 78 Clay and sand (red clay) 128-1 48 feet.— __ Below -71 320 76 Below —244 St. Elizabeths Hospital (1907) — - — — ____ — 590 10 "Arkosic material" 400-440 feet, probably -390 rotten rock; crystalline rock 440-590 feet. Do__ —— — — —— — ——— — __ ————— 398J. 10 Granite at 397 feet ______-387 St. Elizabeths Hospital, 1 mile east of 1 600 160 "To rock" ______-440

Maryland PRINCE (5EORGES COUNTY [See also pages 29-31]

68 35 -10 Hyattsville: West of railroad station (Meyer Lewin)__. 206 50 Coarse water sand, 200-206 feet- ______285 Sand at 285 feet _ ___ . ______247 12 Granite at 247 feet deep ______-235 242 20 Rock, 234-242 feet ______-214 University of Maryland: College Park ______284 145 Quartz 191-193 feet; gneiss 193-284 feet___ -46 180). 60 Hard green rock, 154-180}^ feet ______-94 Beltsville, Agricultural Research Center: Al. No. 2 (1934) — ______425 160 Rock at 315-425 feet ______-155 F. D. No. 1 _____ — _ ———— ————— —— 260 125 Rock at 260 feet ______-135 Hole "N"______———— ——— ______359 157 Rox;k at 307 feet______.-______-150 Hole "E"______363 130 Rotten rock, 263-272 feet_ _ ___-______-133 D. F. No. 5 (1934)______"______250 126 "Loose rock" at 196 feet; also "rotten rock, -70? 185-197 feet." Beltsville, Agricultural Research Center: 364 150 Gneiss, 228-304 feet__-______.- _ _ _ . -78 Dairy No. 4______251 123H "Sand and broken rock" 215-233 feet, -110 gray rock 233-251 feet. 946 145 To rock under entire thickness of Potomac -801 387 290 Water sand at 383-387 feet______1,400 280 No reliable data, but granite reported. -____ -1, 120 1,728 260 "Reddish-brown sandy clay at bottom" ____ -1,468 1,511 260 Below -1,250 1,000

CHARLES COUNTY [See also page 31]

Indian Head (Naval Proving Ground)- _ 1,200 95 Hard rock 740-1,200 feet.. __._ -_ _ _ -645

1 Not on plate 1. DATA ON BOREHOLES AND EXCAVATIONS 39

Data, on boreholes and excavations, indicating altitude of bedrock—Continued

Depth of Land surface Bedrock surface Location hole altitude Materials altitude (feet) (feet) (feet)

Virginia ARLINGTON COUNTY [See also pages 31-33]

Hoover Airport (amusement park, 1925) L..-. 102 10 Schist at 92 feet ______-82 Hoover Airport (1926) 1 ______. ______330 10 Schist samples from 320 to 330 feet, but no data as to top of rock. Pentagon Building (test holes) ______30-60 10-50 From 13? to -27 American Oil Co., filling station, % mile south 314 10 -104 west of Highway Bridge (1926). McGuire and Rolfe, a few rods southwest of 303}^ 10 Fill 0-62, sand 62-105, bedrock 105-303^ -95 American Oil Co. feet. Oxygen Co.1 ______97 15 Below -82 Norton Rendering Co. (1933) *.. ______355 10 -85 Abbatoir (1920).______480 30 -55 Columbia Pike, corner of Highway No. 1, 125 12 Bedrock at about 105 feet ______-93 1920.1 Jefferson School ______130 150 18th St. near Arlington Ridge Road, south 163 100? No bedrock reported to 60 feet or more Below -60 west of Hume School. below sea level.

ALEXANDRIA [See also page 33]

Alexandria, Pendleton and St. Asaph Sts. 430 30 Did not reach bedrock.. ______Below —400 (brewery). Alexandria, Union and Cameron Sts. (ice 401 10 _____do_-__-___--__-- ______Below —39 plant). Alexandria tunnel to Marbury Point (pro 201 Mud, sand, and clay. Did not reach posed, 1941 ; 2 holes. bedrock.

FAIEFAX COUNTY [See also pages 33-34]

Seminary Station, % mile north of (just north 240 230 240 feet of casing. All Potomac group. Below -10 of old Fort Crawford). Theological Seminary, }'\ mile southeast of _ 150 200 Below 50 Episcopal High School.- ______300 260 Episcopal High School, yz mile north-northwest. 170 260 Granite 165 to 170 feet ______95 205 272 Below 80 Lincolnia, % mile south of ______117 247 Ends in Potomac group ______Below 130 Lincolnia, % mile west of ______93 228 _____do._ — — — — — — __ — — — — _ Below 135 Do_____-______.______125 240 _____do______-___-______.__-__- Below 115 72 270 __ _ do__._-_ _ _-___--_-______._ Belo^- 198

1 Not on plate 1.

INDEX

Page ' Page Abbatoir, Arlington County, Va._. ______.______39 Forestville, Md....._————————————————„__._.....—.„ 30,38 Accotink, Va______.______. ______.______34 Fort Belvoir, Va...... ——...._...... ——.— 34 Acknowledgments______..______1-2 Fort Hunt, Va._.__————•———— —_...... r—— 34 Agricultural Research Center, Beltsville, Md_. ______.______30,38 Fort Washington, Md...... -.-_„„—— ———————_.....„..„ 30-31,38 Agriculture Department Building______.______-.. 27,37 Fossil wood, occurrence.--.------____--..——————--—— —— — — --- 18,23 Alexandria, Va______.______33,39 proposed tunnel to Marbury Point..-.__..______33,39 Gales School (old)....—.——...—.—.———..——.—.-—-..——.-.— 35 Alluvium, character and distribution.....__.______.______4 Geologic history_...... _.———_—.....——_————...—————— .... 5,7-8 Altitude datums______.______.______2 Geology of the area...... ————...... __._...... 1, 2-5, 8, 20, 27, 28, 31, 33 pis. 3-5 Ambassador Hotel. ______.______36 See also discussions of particular sites. American National Red Cross Buildings...___.______.. 10,11,36 Glenn Date, Md——————— ——————————————— 30,38 American Oil Co. filling station, J$ mile southwest of Highway Bridge (1926).. 31,39 GoldcraftCo... ————————————————————— ——— 37 Apex Building______.______.______. ______.. 8,35 Granite, character and occurrence.__._. ——..-..——.—————— ...... 3 Arlington County, Va..._...... __.__...... _.._... 31-33,39 Granite gneiss, character.. _———...... _——————.—— ———-—————.. 2-3 Arlington Memorial Bridge______.______..______25,37 Greyhound Lines..----. —— -.. —. ... —— ————— ----— ... — ---- —— - 35 Artesian water, source______. ______3 Artificial fill, occurrence.______.._____... 5,20 Hamilton Hotel.————— — ——— ——— ——— ——————————— 36 Atomic Energy Commission..__.....______12, pi. 8 Harrington Hotel....-______-______-—___—_-----—— 17,35 Aurora Hills, Arlington County, Va______.______. __ 31 Harvey's Restaurant (old)-—...... —.._——_..—... —————.————— 35 Highway Bridge..... — ———————————— — — —— ———— 21,37 Bedrock, age and character__.______. ___ 2-3 Hoover Airport (old), Arlington County, Va------——...—— —..-. —— —— 31,39 altitudeof-——————————————————_._ 1,34-39, pis. 1,2 Hot Shoppe, 1400 Rhode Island Ave. NE———— —————————. — 37 configuration of, importance of knowledge of.______1 Hyattsville-- —————— —————- — -— — —— —— —— -—- 38 map snowing______.______pi. l 2301 BladensburgRoad—-————————— ——————————— 37 contacts..______.______5-7 Hyattsville, Md..———————— — ..———— ———————————— 29,38 decay of..______..______..______2,7 Hygienic Ice Works..———————— ——————...___.„ — _„———— 27,37 deformation of...—______7-8 exposures of--...——___. ___—___. ______. ______3,8,33 IndianHead, Md-_.———————..————————————— 31,38 See also discussions of particular sites. Information, sources... —— _-_..-...-.. —— ——.... — .— ——— ——— —— —— 1-2 Belasco Theater (old)—...... _..—..„.—...... 36 Interior Department Building———.—— .——.—— ————.——— 10, 36, pi. 8 Beltsville, Md.._...... _———————————..._....__.-.-.. 30,38 Internal Revenue Bureau Building_____——__——__ ——— — 8-9, 35, pi. 7 Boreholes and excavations, data on__. ___.______.______34-39 Interstate Commerce Commission Building—------——__— — . —.. 9-10 35, pi. 7 See also discussions of particular sites. Ivy City shops of Washington Terminal Co.------——— —— — 28,37 Brightwood to Silver Spring, bedrock contact______... 6 Jefferson Memorial.------_—.————...—------...... ——.—— 25,27,37 Cairo Hotel_.____.______.______.. 36 Jefferson School, Arlington County, Va.....--.---. — ————— —. — — ------39 Calvert formation, character and distribution____.______4, pi. 3 B Judiciary Square..-----————————-——————...... —————.———— 15,17 Calvin Coolidge High School_...... _...... ______..___ 20,35 Julius Garfinckel & Co.. — .—- — —————— — — ———— —— ——— 35 Carry Ice Cream Co-___.______.______38 Juvenile Court...-...- —— — —— —— ——...- —————— ----- — —... — --— 17 Center Market (old)...... ____._...... ___—_.______35 Central Theater...... _...... _.__ ...... 35 Keith's Theater....——————————————————— — ——— — ——— 36 Chapin-SacksCorp-.--..... —...... _...... 27,37 Kresge Co., S. S., llth and G Sts. NW...————————————————— 35 Charles County, Md...____.._._....._...... _ ...... ^... 31,38 7th St. NW., between D and E..- ——————————— ———————— 35 Chesapeake & Potomac Telephone Co., 14th and R Sts. NW...... 17,36 725 13th St. NW_—____...... 35 7th St. NE., between A and B Sts—....—...... _ 27,37 Labor Department Building-..——-—— —— - —.- — —— — — —— 9-10, 35, pi. 7 Chesapeake group, character and distribution....______.._____.. 4 Langdon———————————————————————————————— 28,38 Ohillum gas tanks, Md.__.______.______...______.. 29,38 Lincoln Memorial——— —. —— — .———— —————— — ——— — 23-24,37 City Post Office Building ^old)...... —...... &, pi. 7 Lincoln Park.__....___-__..___..—...———— ——— -————— 37 College Park, Md ...... 29,38 Lincolnia, Fairfax County, Va.... —— .——. ———— ————— — — —- 39 Colonial Ice Cream Co. ______.. 28,38 Lydecker Tunnel—...——————————— — ————————— 18-19,36 Commerce Department Building.______._ 10,36, pi. 7 Corby Co...... ___...... _._...... _...... __..___...—.. 28,38 McGuire and Rolfe borehole, Arlington County, Va——__._.__ ———.. 31,39 Corcoran Building (old)..______.______.______36 Magothy formation, character and distribution.————————.——————— 4 Court of Claims Building______.______.. 10,12 Maryland..-..-.--_-_-_...——————_.—— .——.—.„__... 29-31,38 Cretaceous rocks, character and distribution...______..______3-4 Mayflower Hotel and vicinity..-...-.-—.—„_—————.....——— 17-18,36 Meadows, Md... ————————————————————————— 30,38 Diorite, character and occurrence... ______3 Memorial to the Women of the Civil War..—————.——.——-———————— 10 District of Columbia...... 8-29 Miocene rocks, character and distribution.--- —— — —. ——— — „..— 4. pi. 3, B rocks of._____.______.______8,20,27,28 Monmouth formation, character and distribution— — — —.. ————.——— 4 Mount Vemon.------_. — _...._—-———— —— - ——— —————— — 34 Eocene rocks, character and distribution...______....______4 Municipal Center, proposed site—_-._.... —— ----- — —— —— —— — —— 15,35 Episcopal High School, Fairfax County, Va..—.__...._._____... 33-34,39 Murphy Co., G. C., 14th Street NW., near Irving Street....—————— .... 17,36 Ericsson Memorial. ______.______37 1214 Q St. NW———————— ——————— — ————————— 35 Evening Star Building______.______9 National Academy of Sciences------..---.------—------13-14,36, pi. 8 Fairfax County, Va...... ___...... _...... ___.... 33-34,39 National Archives Building.-- —— .„...... „.....———...———— 8, 35, pi. 7 Fairfax Farms Milk Co...... —...... _...... _._...... 15 National Training School for Boys.—.... ———————— -----—. ——— ----- 38 Faults, occurrence.._____....______..______8, pi. 6 Naval Gun Factory-....————————— —————— —— . ——————— 28,38 Federal building site between llth and 14th Sts. SW., C and D Sts.—.___ 26,27 Naval Proving Grounds, Indian Head—...... — — —— —... —.—————— 31,38 Federal Reserve Board Building..______13,36,pi.8 Navy Department Building—--———„—— — ——-————— 14-15, 36, pi. 8 Federal Trade Commission______.______8,35 Norton Rendering Co., Arlington County, Va——...—...——..__„.—-,.- 31,39 41 42 INDEX

Page Page Oxygen Co., Arlington County, Va. 31,39 Standard Brands, Inc______-______-____._____ 28,38 Stanton Square_.__....———..———-————~————..—————— 37 Pabst Brewery (old) _____.______.__. ______37 State Department Building——...——..———„„.——.—------15,16,36, pi.8 Palais Royal (former site)-____.______.______.. 17,35 Suitland,Md——.—————--—————-———--.—————— 38 Pamunkey group, character and distribution______.______4 Pentagon Building...___„_____-__.___.______.___31-33,39 Takoma Park to Paint Branch, bedrock contact..———————..—————— 6 Piney Branch relief sewer.. _... __ —__——__—_._____.___.... 19-20 Temporary BuUding 4, 20th and 21st Sts. NW., C and D Sts——... 12-13,36, pi. 8 Pleistocene rocks, character and distribution.....__._.__...__ __ 4 Tenleytown Ridge, bedrock contacts.—— ————————.„___—... 6 Police Court.----.--.-.------_.—————— ——— ——— —— _ ————_ 17 Terra Gotta...... ————-——————.———..—.—_._————— 38 Post Office BuUding (old).-- — ——— ——— --——————————_ — — 9, pi. 7 Terrace deposits, character and distribution—..... —————._..,— 4,20, pis.4,5 Post Office Department BuUding..------.——————-__——. 9,35, pi. 7 contact of, with bedrock—------—.. —— - —— ——— ————— — - ——.. 7 Potomae group, age, character, and distribution...-..__..._..-._ 3-4,31,pi.3 Tertiary rocks, character and distribution...... —— —— .„——_ — — _.— 4 contact of, with bedrock-..-.__--..._---. -----__------__..___- 5-6 Theological Seminary, Fairfax County, Va.-_- —— — —. —— _————— 39 water in.-.-,._...... ——...... ———__—..—__..__.._.. 3 Thompson's Dairy.._ —————.————————————————————— ——— 35 Prince Georges County, MA...... ————————__...... 29-31,38 Triangle area, 7th and 15th Sts., Constitution Ave. and Pennsylvania Ave— pi. 7 Public Health Service Buildings...._...... -....—__...... 12, pi. 8 University of Maryland.. ——.... ——————————————.———————— 29,38 Quaternary rocks, character and distribution...-..-- ...... __...... 4 Upland gravels, character and distribution— ——————.————————... 4 Railroad Bridge.-..--.------._———— ——— -_——._...... _ 20-21,37 Virginia...-—------—————--—————. — -——————- 31-34,39 RaleighHotel.... —. ——— ——— ———————————— —— —— —— 9 Raritan formation, character and distribution....--.------.__.___.__ 4 WakefleldDairy....—— — .— — ——————— ————————— 38 Red Cross Building..-.-.-.-----.-----.------.-...----.-. 10,11 Warner Building__.————.—... ————————.———_——. — — 9 Reflecting Pool------.------.------.------.------.------_.--.---. 23,37 Washington, lower part, bedrock contact.. ——— „_ ——.—...——.—— 7 RiggsHouse, old. — ..-- —————————————— ——— — ——— ——— 36 Washington, northeast section—...—— ——— —— - —— —————... — — 27-28,37-38 Rocks of the area.__— ————————— — —— 1,2-5,8,20,27,28,31,33, pis. 3-5 Washington, north west section.—-. —. — ———— _..——-..._——. 8-20,35-36 See also discussions of particular sites. Washington, southeast section.___.__.______.___.____ 28-29,38 Washington, southwest section....-.-——....—— —..—.—.——- 20-27,36-37 St. Elizabeths Hospital—— —— .—-— —.—„ — .—....__—___ — . 28-29,38 Washington Gas Light Co., old building——————_——-—_—_ .-.. 17,35 Sears, Roebuck & Co., 911 Bladensburg Road.-—._____..._...... 37 Washington Hotel__.__...... —„__. —— ————————_——... 36 Security Storage Co...... ———„———-————————.———-—------—— 35,36 Washington Monument------———..—————. —— .-——————— 20-23,37 Sedimentary formations, character and distribution...—_—..... 3-5,8,20,27,28,31 Washington Navy Yard..-.-,------——------—...... —...... 28 See also discussions of particular sites. Washington Terminal Co——.—___ ———————__———„„_—..__——. 28,37 Seminary Ridge, Fairfax County, Va_...——...... —------33-34,39 Water-bearing formations-————-—..-.. ———..—————.————— 3,6 Seminary Station, Fairfax County, Va.-—-——....~ ———. — ...... -.. 33,39 WaterGate——..——— ——— —— ————————————— 23-25,37 Shoreham Building_—————_. — — -,.————.——————————————— 36 Water supplies, source_—.———————— -——————. ———... —'———— 3,6 Sibley Memorial Hospital...- — .——. ———— — .—„—.—... — .—— 35 Womens World War Memorial Building______10,11 Soldiers'Home.--—---...------.----———....—.———.—— ——— 18,36 Woodridge...—————————————————.———————— 28,38 Sources of Information. —. — - — — — — —... — ——— - —— — - —— -— 1-2 Woodward & Lothrop, North Building———————_—__..._____... 17,35 Southern Dairies------.------.------—------37 Woolworth Co., F. W., 12th and F Sts. NW———...... _.———————__ 35 o