Toronto and Scarboro' Drift Series. — Uphain. 313 
house, a mile or two north of Toronto. Amnicola Hmosa, a Succinea, 
and fragments of another species. These occur at 220 feet above the 
lake, but the sand containing them runs up to 247 feet and may cor- 
respond to the silty sand between till No. 2 and till No. 3 at Scar- 
boro'. 
One of the recessions of the ice, perhaps the one just mentioned, 
appears to have been very extensive, for two thick beds of boulder 
clay are found to be separated by stratified materials at numerous 
points on the lake shore as far east as Newtonville, fifty miles from 
Toronto. The same relationship is found near the head-waters of 
the Don, about eieht miles north of the city, and also in ravines to 
the east, but has not been observed to the immediate west ; though 
the stratified clays lying between two layers of till at Dundas and 
at several points near Niagara Falls may correspond to the same 
interglacial stage. In that case the ice must have withdrawn eighty 
miles in a northeasterly direction before advancing again. 
* * * "pi^g highest boulder clay has not yet been traced with cer- 
tainty west or south of the Toronto region, however, since the four 
sheets of boulder clay are very much alike and cannot be discrim- 
inated when found alone; and there is a possibility that it ends here, 
and that the water then filling the Ontario basin was continuous with 
that of some of the successors of lake Warren. 
In several earlier papers, treating of the causes of the Ice 
age, I have attributed the snow and ic'e accumulation to great 
uplifts of the land areas which were glaciated, giving tO' them 
a cool and snowy climate throughout the year. From the 
depths to which preglacial land valleys are now submerged 
beneath the sea level on the coasts of North America and Eu- 
rope, it is known that the elevation of the glaciated portions 
of these continents was 3,000 to 5,000 feet higher than now. 
After a very long duration of the somewhat fluctuating 
ice-sheet on each of these continents, the glaciated areas sank 
to their present hight or mositly somewhat lower, so that 
when the ice melted away the sea covered coastal portions of 
the drift-bearing countries. The great change of climate re- 
sulting along the borders of the ice-sheet on account of the 
land depression caused rapid melting there, and this advanced 
inland until all the ice disappeared. The depression from the 
former high altitude, as was remarked by Dana, would trans- 
fer the southern part of the ice-sheet from a climate like that 
of Greenland to the temperate climate of southern Canada 
and the northern United States. Marginal melting then grad- 
ually pushed Imck the l)oun(lary of the ice and thus gave to 
