Page:The American journal of science, series 3, volume 49.djvu/33

Rh Lteelevation of the St. Lawrence river basin. 15

Indeed, the outflowing river from Lakes Iroquois, Hudson- Champlain, and St. Lawrence, or the Hudson during the Post- glacial period, channeled the lower part of this valley to a depth of about 100 feet below the present sea level, proving that the land there, as Merrill points out, stood so much higher than now at some time after the ice retreated.

According to the observations of Davis, Baldwin, and Baron de Geer, the highest shore line of the Lake Hndson-Cham plain is now elevated to about 275 feet above the sea at Catskill, 1ST. Y. : 550 feet in Chesterfield, N. Y., on the west side of Lake Champlain opposite to Burlington ; and 658 feet at St. Albans, Vt. Assuming that the mouth of the lake, near New York city, was 50 feet above the sea, the differential northward up- lift of the originally level shore has been at the rate of about two feet per mile for the 100 miles from the present mouth of the Hudson to Catskill ; 1*7 feet per mile for the next 160 miles north to Chesterlield ; and about three and a half feet per mile in the next 30 miles north-northeastward to St. Albans. Perhaps a higher beach may exist in Chesterfield, which would bring these gradients nearer to uniformity. The series noted there by Baldwin comprises eight beaches refera- ble to the successive water levels of Lake Hudson-Champlain, Lake St. Lawrence, and the sea in the Champlain basin, their heights above the sea level of to-day beino; 550 feet, 530, 470, 423, 386, 365, 335, and 290 feet The mean level of Lake Champlain is 97 feet above the sea, and its maximum depth 402 feet. The lower four of these beaches belonged to the Champlain arm of the enlarged Gulf of St. Lawrence, as shown by the height of its sand deltas and associated fossiliferous clays ; but the higher four represent stages of the Lakes Hud- son-Champlain and St. Lawrence. These shore lines, like those of the glacial lakes farther west to Lake Agassiz, were probably formed during times of rest or slackening in the somewhat intermittent epeirogenic elevation of the land.

Lake St. Laiorence* — The records of the Glacial and Cham- plain epochs in the St. Lawrence valley have been most fully studied during many years by Sir William Dawson, to whose work chiefly we are indebted for detailed descriptions of the evidences of the marine submergence of that region to a maxi-

maps and sections, views of scenery, and nine plates of Pleistocene fossils. This volume sums up the author's work since 1855 on the glacial drift and associated lacustrine and Champlain marine formations of the St. Lawrence valley, embody- ing the studies which had been published in many papers in the "Canadian Naturalist and Geologist " and elsewhere. He had given a similar summary in a pamphlet of 112 pages, " Notes on the Post-pliocene of Canada." in 1872. J. W. SpeDcer. G-. K. Gilbert, Baron de Geer, S. Prentiss Baldwin, and Warren Upham, as before cited for Lakes Warren, Algonquin, Iroquois, and Hudson-Champlain.
 * Sir J. William Dawson, The Canadian Ice Age (Montreal, ]893), p. 301, with