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Historical Bedrock Maps of Maine
|Geological Map of Maine
Charles H. Hitchcock
|Images of the map:|
|Medium (814 kb, gif)||Large (2.9 Mb, pdf format)|
|Map legend and title (257 kb, gif)|
|Images of the explanatory text:|
|Medium-sized files||atlas title page (1 Mb, gif)|
|Page 1 (774 kb, gif)|
|Page 2 (987 kb, gif)|
|Page 3 (957 kb, gif)|
|Page 4 (257 kb, gif)|
|Large-sized files||Full text (7.7 Mb, pdf format)|
Results of the Maine Scientific Survey of 1861 and 1862 were
described in two lengthy reports and embodied in a large Geological Map
of Maine presented by C. H. Hitchcock to the State Legislature. The map
was exhibited by special permission to the American Association for the
Advancement of Science in about 1868 and an abstract of the explanation was published in the AAAS proceedings. Unfortunately, the whereabouts of the original map is not known. Hitchcock produced a smaller, page-sized map that was published in 1885 as part of Colby's Atlas of the State of
Maine. It is based largely on his original 1868 map, though his
accompanying text indicates some amount of modification. The Colby
Atlas was widely circulated in several printings. Each map was colored
by hand. This is one of the finer copies that has survived.
Hitchcock considered this to be a preliminary geologic map. In 1861 he wrote that his original map did not warrant publication since it was so imperfect, but he presented a manuscript copy so that "the total results of all previous explorations will not be lost." Considering the complexity of Maine's bedrock geology and the brief time of study available the 1885 map is remarkable, a testament to Hitchcock's knowledge of geologic principles and his skill at synthesizing an insufficient amount of data into a reasonable interpretation.
Geographic Index to the Figures.
The broad aspects of Maine's bedrock geology are essentially correct. The Silurian and Devonian formations of northern Maine are shown to occupy continuous, northeast-trending tracts (Figure H1). Calcareous slates, indicated as "Upper Silurian", are mapped from Houlton to Fort Fairfield (Figure H1). The complex metamorphic and migmatitic rocks of western and southwestern Maine are set apart, as are the metamorphic rocks extending from Harpswell through Waldo County, although the names "Montalban" and "Laurentian" mean little to modern geologists (Figure H2). The broad lowland area of the central Maine slate belt is delineated, with a patch of Silurian "clay slate" around the controversial Waterville fossils (Figure H3). Large areas of granite had been discovered in Hancock and Washington Counties, at Katahdin, and to the south of Sebago Lake (Figure H4), even though scholars of the day did not agree as to how such masses of granite had formed.
Where more detailed mapping had been done, mainly in the populated regions, comparison with subsequent bedrock maps shows the enduring quality of the work. Notice, for example, the Upper Devonian red beds near Eastport (Figure H5A), the accurate contacts of the Lucerne, Deblois, and Sedgwick granites near Blue Hill (Figure H5B), the Androscoggin Lake pluton west of Augusta (Figure H5C), and the oval outlier of "Upper Devonian" sandstone west of Presque Isle (Figure H5D). By contrast, the geology of the "Wild Lands" of northern Maine was known only in reconnaissance from bateau and canoe expeditions up the major rivers. It is obvious from the blank area in northern Hancock County, and the sweeping shapes of the contacts in northern Franklin and Somerset Counties that the geology was poorly known in those areas (Figure H6).
By 1861, paleontologists had correctly established the ages of the Upper Devonian Old Red Sandstone at Perry, certain Lower Devonian sandstones and Upper Silurian rocks of northern Maine, and fossil-rich Upper Silurian rocks at Pembroke. Incomplete or problematic fossil collections from Flint Island in Narraguagus Bay and from Waterville suggested Lower Silurian ages for those places also.
Despite the circumstance that "fossils are wanting" elsewhere, Hitchcock assigned most of the remaining rocks to the Lower Paleozoic, relying on the principles of stratigraphic continuity and superposition combined with a knowledge of western New England geology to deduce the ages of Azoic rocks from the ages of fossiliferous ones. A significant conclusion presented on this map is that all of the bedrock in Maine is older than Carboniferous. Therefore, the Carboniferous coal measures being mined at the time in Massachusetts and in New Brunswick do not occur in Maine. "We did not desire to arrive at this conclusion, but the inference must be drawn." (Hitchcock, 1861, p. 255)
Metamorphic rocks of southwest Maine are shown as Montalban and Laurentian (Precambrian), even though Hitchcock allows that "It is difficult as yet to say whether any of these Azoic rocks belong to the Laurentian series or the Paleozoic system." No Ordovician rocks are shown because it was not yet an accepted geologic time period. Rocks we would now call Ordovician were included in the Lower Silurian of Hitchcock's time.
Belts of rock of the same age are repeated across the map, especially in northern Maine, due to large anticlinal and synclinal folds (Figure H7). The overlapping pattern of units on the map indicates major unconformities beneath the Middle Devonian, beneath the Upper Silurian, and beneath the Lower Silurian (Figure H7). Relationships among Huronian rocks, Laurentian rocks, and granites are ambiguous.
Differences between the various bedrock maps of Maine derive partly from the amount of information available at the time of publication, but depend more importantly on the perspective of the author. Charles Hitchcock was one of the preeminent geologic scholars of his day, with a vast knowledge of New England geology. His 1885 map is clearly an attempt to generalize the major geologic features of Maine into a stratigraphic or historical perspective. In his explanatory text, Hitchcock mentions many geologic details that demonstrate his command of the facts. But this map is not intended to show all those details. Rather, it gives a larger view of the systematic nature of Maine's geology, related to the geology of neighboring areas and explained by the workings of geologic processes through time.
Hitchcock, Charles H., 1861a, General report upon the geology of Maine: in Preliminary report on natural history and geology: Maine Board of Agriculture, 6th Annual Report, p. 146-328.
Hitchcock, Charles H., 1861b, Geology of the wild lands: in Preliminary report on natural history and geology: Maine Board of Agriculture, 6th Annual Report, p. 377-419, map.
Hitchcock, Charles H., 1862, Geology of Maine [includes contributions by G. L. Goodale, O. White, and E. Holmes]: Maine Board of Agriculture, 7th Annual Report, p. 223-430, map.
Hitchcock, Charles H., 1868, Explanation of a geological map of Maine: American Association for the Advancement of Science, Proceedings, vol. 16, p. 123.
Hitchcock, Charles H., 1885, Geology: in Colby's Atlas of the State of Maine: George N. Colby & Co., Houlton, Maine, p. 14-17.
Hitchcock, Charles H., 1885, Geological map of Maine: in Colby's Atlas of the State of Maine: George N. Colby & Co., Houlton, Maine, p. 27 (scale approximately 1:1,267,200).
Text by Henry N. Berry IV
Graphics by Marc Loiselle and Henry Berry
Originally published on the web as the June 2004 Site of the Month.
Last updated on April 11, 2012
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