DESCRIPTION OF THE PENOBSCOT BAY QUADRANGLE By George Otis Smith, Edsoii S. Bastin, and Charles W. Brown. INTRODUCTION. phosed sedimentary rocks near the Quebec-Maine are produced in the processes of metamorphism. Silurian sediments lie unconformably upon the boundary, as well as to metamorphic rocks in New Weathering and stream erosion acting on these rocks eroded surface of the North Haven greenstone, and LOCATION AND PRINCIPAL TOWNS. Brunswick, further confirms this age determination. before the advent of the glaciers sculptured them are followed in apparent conformity by the Thoro- The Penobscot Bay quadrangle lies between Associated with the schists and slates, both on into a succession of hills of greatly varying size and fare andesite, which in turn grades upward into the meridians 68° 30' and 69° west longitude and par­ the Maine coast and in the northern part of the slope and irregular form. There is a complete Vinalhaven rhyolite. All these rocks, from the allels 44° and 44° 30' north latitude. It includes State, are fossiliferous sediments of Silurian and absence of plateaus, monadnocks, or any other fea­ oldest to the youngest, are cut by granite of prob­ one-fourth of a square degree of the earth's surface, Devonian age, whose unmetamorphosed character tures indicative of cycles of erosion. able Devonian age, with associated diorite, diabase, and contains 857 square miles. The quadrangle shows that the principal epoch of folding occurred The eroding and depositing action of the glaciers and gabbro. embraces nearly the whole of Penobscot Bay, about before their deposition and probably closed the reduced to some extent the irregularities of the hills SEDIMENTARY ROCKS. one-half its area being water. It lies about mid­ Ordovician. To this date, therefore, is assigned the by planing off the more jagged prominences and way between the eastern and western boundaries dynamic metamorphism which has affected all the filling some of the depressions, but the resulting ELLSWORTH SCHIST. of Maine, and includes parts of Knox, Waldo, and pre-Silurian rocks and produced structures which contours were still very irregular. Definition. The Ells worth schist is composed Hancock counties. Of the land, about two-thirds differentiate them from the later formations. In The majority of the hills do not rise more than 200 of highly metamorphic argillaceous sedimentary belongs to the mainland and the remainder to the coastal region of Maine granitic intrusion on to 300 feet above sea level. Higher elevations are rocks, prevailingly greenish gray in color and islands, which are extremely numerous and of a large scale has resulted in some contact metamor­ usually called " mountains," though many of them locally much injected with quartz. They are various sizes, the largest being North Haven, phism of Silurian rocks, but this is readily distin­ are only 400 or 500 feet high, and the name is to named from the city of Ellsworth, just beyond Vinalhaven, Deer Isle, Isle au Haut, and Isles- guished from the dynamic metamorphism of earlier some extent justified by the abruptness with which the northeast corner of the quadrangle, near which boro. Belfast, the largest- town, with a population date. many of them rise from the shore and by a certain locality occur abundant exposures typical of the of about 5000, is the county seat of Waldo County The igneous activity which especially character­ magnification due to the prevalent haziness of the formation. and the terminus of the Belfast branch of the izes this province began with the volcanism of atmosphere. The highest hill of the region is Blue Distribution. From the village of Surry, in the Maine Central Railroad. Stockton Springs and Cambrian time, volcanic rocks probably of this age Hill, near Bluehill village, which rises to an eleva­ northeast corner of the quadrangle, the schists Searsport, the only other railroad towns, are the being known both on the Maine coast and in east­ tion of 940 feet. extend toward the west and southwest for 2 or 3. southern termini of the Bangor and Aroostook ern Massachusetts. In the Silurian the volcanic The present drainage of the region is most miles, until the Toddy Pond granite area is Railroad. The Penobscot Bay region, because of activity again prevailed and was followed probably irregular, partly as a result of the preglacial irregu­ reached. The largest continuous area within the its great beauty, its cool summer climate, and its in Devonian time by the intrusion of granitic rocks larities in the form and distribution of the hills and quadrangle has a width of about 2 miles, west of many bays and inlets, which afford safe harbors already referred to. It is this abundance of vol­ partly as an effect of the blocking of the preglacial Toddy Pond, and from that locality extends south­ and protected sailing, has come to be one of the canic and plutonic rocks of Paleozoic age that char­ stream courses by deposits of glacial drift. Most of ward to Bluehill, where its width increases to most popular summer-resort regions in America. acterizes both the area here described in detail and the streams are brooks only a few miles in length, nearly 4 miles. The same belt continues along In the touring season most of the business and the whole province. It is noteworthy that these and their courses are in many places irregular and Bluehill Neck, widening southward until it occu­ resort towns are easily reached by steamer from granites do not form a part of an Archean protaxis, obstructed by ponds or marshes. Water power is pies the whole width of the Brooklin peninsula. Boston, Portland, or Rockland. Castine receives, as formerly held, but represent relatively late available along some of them, but its importance is It is cut off by the granite just north of the village perhaps, the largest number of summer visitors, intrusions. not great. All the so-called "rivers" of the quad­ of Brooklin, but on the south side of Eggemoggin Reach, on Deer Isle, what appears to be a contin­ but Dark Harbor (Islesboro), North Haven, Blue- TOPOGRAPHY rangle are in reality tidal estuaries. Bagaduce hill, and many smaller places are popular resorts. River, one of the largest estuaries, is remarkable for uation of the schist belt is represented by two small The most striking features of the topography of the northwestward trend of its upper portion as con­ schist areas, one on each side of the serpentine stock. GENERAL GEOGRAPHY AND GEOLOGY OF THE this quadrangle are the large number of islands and trasted with the southwestward course of the lower Farther east the schist reappears on the northern PROVINCE. the exceedingly irregular form of the coast line, portion. Through the portion called the Narrows part of Long Island and in small isolated areas The State of Maine belongs to a geographic and features that are characteristic to a greater or less the tide runs with a force capable of generating a along its western and southwestern shores. Several geologic province which includes the most of New degree of the whole Maine coast. This irregularity large amount of power if means can be devised for small masses occur within the granite area east and England, together with Nova Scotia, New Bruns­ can not be accounted for by the eroding action of its conversion. A similar water power is available southeast of North Brooksville. wick, and the Eastern Townships of Quebec. the ocean, for it is as marked in the protected coves near Bluehill Falls, at the outlet of Salt Pond. Structural relations. The rocks of this formation Topographically the province is characterized and estuaries as in ;the parts which are exposed to are nearly everywhere highly schistose and show by considerable diversity of forms, but for the the full violence of the storm waves. A glance at DESCRIPTIVE GEOLOGY. but slight lithologic variations in different parts of most part it is an upland or plateau region, bor­ the topographic map shows the presence of certain STRATIGRAPHY. the region. They have suffered much more intense dered on the one side by the great Atlantic Ocean long, narrow channels which are largely free from crumpling and shearing through regional metamor­ INTRODUCTORY STATEMENT. depression and on the other by the great Canadian islands. The most conspicuous of these is followed phism than any other rocks of the quadrangle. highland region. The higher portions of this by the eastern boundary line of Waldo County; The geological description of the Penobscot Bay Distinct indications of bedding in the schist are upland country are deeply incised by the rivers others are Bluehill Bay and Eggemoggin Reach. quadrangle embraces a study of unmetamorphosed wholly wanting within this quadrangle, but are and streams, so that they flow-in deep valleys or The Coast and Geodetic Survey chart of the same and metamorphosed representatives of both sedi­ found at one locality a few miles to the east. canyons. Rising above the highest parts of the region, on which the depths of water are recorded, mentary and igneous rocks. The unmetamorphosed The general strike of the schistosity is rather New England plateau are the White Mountains, shows that these are deep-water channels and are sediments have a very small areal distribution and constant, and trends north of east, N. 55°-60° E. the range of lower peaks in western Maine, and therefore the principal paths of navigation. include only the Silurian rocks of North Haven^ being about the average. In some localities the Mount Katahdin. The largest channel, the one passing on the east and Stimpson Island. Because of their fossiliferous strike varies from due east and west to almost As a geologic province the region is character­ side of Islesboro, is a direct continuation of the character, however, these roc,ks furnish the basis of north and south, and even within a few feet ized by the presence of great intrusive masses of present Penobscot River valley.