Covering the bedrock platform are unconsolidated deposits associated with the 

 Pleistocene period of glaciation, which began approximately 1 million years 

 ago and ended in coastal Maine from 12,000 to 13,000 years ago (Stuiver and 

 Borns 1975). Reworking of the glacially derived deposits by upland and marine 

 forces has created shoreline, intertidal, and shallow subtidal sedimentary 

 deposits that presently fill the low areas between the bedrock platform highs 

 along the coast (atlas map 3). 



Pleistocene glaciation, deglaciation, and associated deposits . The 

 glacial deposits constituting the surface soils of the upland were laid down 

 by glacial ice or glacial meltwater processes during the last phase of 

 Pleistocene glaciation (i.e., the Wisconsin Age). Approximately 28,000 years 

 ago, a glacial mass covered all of Maine and extended out to the edge of the 

 present continental shelf at Georges Bank (Schlee and Pratt 1970). At the 

 bedrock-glacial ice interface two types of activity occurred: (1) thin (2 to 

 10 m thick; 6.5 to 33 feet) deposits of glacial till were laid down; (2) the 

 bedrock surface was scoured of all loose, unconsolidated cover. 



Approximately 13,200 years ago, the glacier margin receded from its terminal 

 position on the Atlantic continental shelf to about the present position of 

 the coast of Maine (Stuiver and Borns 1975). The subsequent retreat of the 

 ice margin approximately 12,800 years ago to a position about 44 miles (70 km) 

 inland of the present shoreline left the coastal area exposed to subaerial and 

 marine erosica processes. 



Because the earth's crust was depressed by the weight of the glacial mass, the 

 land surface (immediately after glacial recession) was about 400 feet (120 m) 

 below present elevations. This crustal depression allowed much of the land 

 surface to be inundated by marine waters from the Gulf of Maine. Along the 

 coast, the limit of marine incursion stands presently at elevations of 240 to 

 290 feet (973 to 88 m; Goldthwait 1949). 



At higher elevations, meltwater from the receding glacier margin deposited 

 stratified sands and gravels into glacial landforms, such as kames, kame 

 terraces, moraines, eskers, outwash plains, and large deltaic complexes at the 

 shoreline (atlas map 3). Boulders, gravel, and sand on the surface of the 

 glacier were left as a blanket of coarse-textured till and in a few coastal 

 localities were reworked by proglacial climate wind into thin eolian deposits. 



Clays and silts were transported to the ocean, where they settled to form 

 extensive blanket deposits of glaciomarine clay. This clay, ubiquitous at 

 lower elevations along the Maine coast, is called the Presumpscot Formation 

 (Bloom 1963). Late Pleistocene shoreline environments (beaches and spits) are 

 preserved on the upland. These separate till and stratified drift from the 

 marine clay found at lower elevations. 



After the glacial margin receded, crustal uplift took place. By 12,000 years 

 ago, most of the submerged coastal lands were exposed to subaerial weathering. 

 Continued rebound of the land mass lowered sea level approximately 8500 years 

 ago to approximately 197 feet (60 m) below the present shoreline (Schnitker 

 1974; figure 2-18). 



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10-80 



