GLACIAL DRIFT ON MOUNT WASHINGTON. 115 



burden ; and to that time I would refer the complete glacial envelopment of 

 Mount Washington, as well as the transportation of the highest, vevy scanty 

 di'ift on Katahdin. This depression of the earth's crust led to changes of 

 climate, from the rigorous conditions causing glaciation to mild temperatures 

 by which the ice was finally melted ; but at first the subsidence was perhaps 

 attended by an increase in the thickness of the ice, whose surface may have 

 been maintained by the snowfall during a short time, geologically speaking, 

 at its former altitude, while the area of the White Mountains sank the 1,000 

 feet which would envelop the top of Mount Washington in the ice-sheet. 

 The mountain was not thus ice-covered so long that the glacial em-rent 

 could sweep away much of the abundant frost-riven debris, nor conspicu- 

 ously emboss any projecting knobs of rock, nor bring many bowlders and 

 fragments of foreign dj-ift. In the 220 miles from the terminal moraine of 

 Long Island, Marthas Vineyard, and Nantucket, north to Moimt Washing- 

 ton, the slojje of the ice surface therefore averaged in its maximum about 

 30 feet per mile, compared with the present sea-level and heig'ht of the 

 mountain, but was only about 25 feet per mile through the greater part of 

 the Glacial period. It is presumable, however, that in a i^rocess of subsid- 

 ence of the land, only the thickness of the ice-sheet, and not the slope of 

 its surface, was increased when the mountain became wholly ice-covered. 



Supplementing the reports of the Geological Survey of Vermont, Mr. 

 Edward Hungerford published in 1868 a valuable paper on the glaciation of 

 the Green Mountains,^ from which most of the following notes are derived, 

 their order being from north to south. Striae on the summit of Jay Peak, 

 4,018 feet above the sea, bear S. 40° E. Very large transported bowlders 

 occur on the top of Mount Mansfield, with striae bearing S. 23° to 28° E. 

 This mountain, the highest in Vermont, attains the elevation of 4,430 feet. 

 Masses of quartz contained in the mica-schist of the top of Camels Hump, 

 4,088 feet in height, show fine lines of striation, noted in three places, S. 

 10° W., the same with variation to due south, and S. 35° E. It is also to 

 be remarked that the rounded northwest side of Camels Hump and its 

 precipitous clifi^ on the south and southeast afford evidence of glacial 



'Am. Jour. Sci. (2), Vol. XLV, pp. 1-5, Jan., 1868. These and other bearings noted in this volume 

 are referred to the astronomic meridian. 



