PALEOLITHIC MAN IN AMERICA. 21 



tion ; and (4) that the earlier epoch, of cold was the longer, 

 though the cold was the more intense and the climate more 

 variable during the later epoch. 



The latest researches in the Atlantic slope have shown more 

 definitively (1) that the interval of mild climate separating the two 

 cold epochs was from five to ten times as long as the post-glacial 

 interval ; (2) that the cold epochs themselves were brief in com- 

 parison with the inter-glacial and post-glacial intervals ; and (3) 

 that the earlier and longer epoch of cold was attended by conti- 

 nental submergence reaching four or five hundred feet in the 

 la,titude of New York and extending to South Carolina, while 

 the land depression of the later refrigeration was but forty or 

 fifty feet at New York, and scarcely extended beyond the great 

 terminal moraine of Long Island and northern New Jersey.* 



During the first epoch of cold and wet local glaciers formed in 

 the Rocky Mountains and in the Sierras, the Great Basin (which 

 these ranges bound) was flooded and the now extinct Lakes Bon- 

 neville and Lahontan were formed, and into the lakes great vol- 

 umes of sand and silt — the lower lacustral beds of Gilbert and 

 Russell — were swept by the flooded rivers ; at the same time the 

 northern ice-sheet stretched down into the Mississippi Valley as 

 far as the Missouri River, the land was depressed, and both glacial 

 and aqueo-glacial deposits were laid down ; and it was at the same 

 time, too, that the Atlantic coast was depressed until the high 

 hills overlooking New York, Philadelphia and Washington were 

 half submerged, and that the rivers built great deltas of gravel 

 and loam along the shore of the expanded ocean, while the waves 

 dropped shallow-water sediments all over the lowlands. With 

 the interglacial warmth the glaciers of the Western mountains 

 were melted, the lakes were dried, and river - gravels were de- 

 posited by the shrunken streams over and canons were cut into 

 the old lake-bottoms ; in the Mississippi Valley the glaciers re- 

 treated and the drift-plains became forest-covered ; while in the 

 East the land underwent re-elevation, and there was erosion of 

 such extent as to afford a rough measure of the duration of the 

 warm interval. During the later epoch of cold and wet glaciers 

 again formed in the Rocky Mountains and in the Sierras, Lakes 

 Bonneville and Lahontan were refilled — the former to overflowing 

 —and the upper lacustral beds were laid down within them ; the 

 northern ice again invaded the Mississippi Valley and formed 

 two or more drift-sheets, together with the peculiar glacial-mud 

 deposit (or loess) into which they graduate, as well as the great 

 terminal moraine stretching from Ohio to Dakota; and in the 

 East the ice again overrode the Adirondacks and the New Eng- 



* "American Journal of Science" for May and June, 1888; "Seventh Annual Report 

 of the United States Geological Survey," 1888, p. 537 et sea. 



