960 HISTORICAL GEOLOGY. 



The "Green Mountain Giant " at AVhitingliani, Vt., weighs about 3000 tons. 

 W. 0. Crosby has described a bowlder on the eastern border of New Hamp- 

 shire having diameters of 30, 40, and 75 feet, and weighing 6000 tons. In 

 Ohio there is one 16 feet thick, which covers three fourths of an acre. 



From southwestern Vermont, the granite of a high hill, between Stamford and Pownal, 

 which is almost as high as the Green and Hoosac Momitains lying to the east and south- 

 east, was carried southeastwardly over the western sides of these mountains, nearly across 

 the state of Massachusetts. 



Iron Hill of Cumberland, R.I., furnislied bowlders of iron ore for the country south of 

 Providence, to the Newport region, thirty-five miles distant, and thence south of east, as 

 sliown by Shaler, to Gay Head on Martha's Vineyard. 



Large bowlders are scattered widely over eastern Long Island, which are the crystal- 

 line rocks, trap, and sandstone of New England ; and others, over western Long Island, 

 which are from the Palisades and lieights along the Hudson River. South of Lake 

 Superior, tliere are bowlders which have come from the north shore of the lake. 



In this movement of the glacier the transported stones and earth, at first 

 intraglacial, have sometimes become superglacial, about any emerged or nearly 

 emerged mountain peak, as in Greenland about the "Nunataks" (page 

 249). And after serving as a superglacial moraine for awhile, the whole may 

 have sunk away through crevices or crevasses to intraglacial positions again. 

 The ice, as it moves up a long slope of a hill or mountain-side, slips over the 

 rising surface, and carries its load with it ; and on many slopes such stones 

 are found at a level 1000 to 3000 feet or more above their source. Mount 

 Katahdin in Maine has many bowlders on its northern face derived from 

 the Devonian rocks of the low country to the north, 3000 feet below it in 

 level, which were thus carried up the mountain. Stones from a low level 

 in the ice may thus, if not stranded on the slopes, use the high level for 

 further travel or continue on at their original level. 



3. Deposition. — The deposition of the transported material took place 

 (1) through crevasses and crevices, aided by descending waters from the 

 superficial lakes or streams; (2) from the melting bottom of the glacier; 

 (3) from the melting always in progress along the front of the glacier, 

 which was augmented during retreats. Moreover, the material pushed along 

 by the glacier Avas an important addition to the moraine-making debris set 

 free by the melting ice. Great bowlders would be the first landed from the 

 decaying ice-mass ; yet large and small stones, earth and clay, are so mingled 

 in the till that the term bowlder-clay is well applied to the larger part. The 

 stones of the till show their glacier origin usually by marks of abrasion. 

 But flowing glacial waters carrying sand have often worn smooth the glacier- 

 dropped stones and bowlders. The subglacial waters, wherever in gentle flow 

 along their valleys, may have made part of the local deposits of clay and sand, 

 while others were made by the waters flowing away from the front. 



4. The terminal moraine or sonther^imost Ice-limit. — The terminal moraine 

 marks the limit of the ice-sheet when it was of maximum extension, and 

 therefore when of maximum power for work, whether at abrasion, corrasion, 



