1903-4. | A Forty-MILE SECTION OF PLEISTOCENE DEPOSITS. 7p 
THE TILL SHEETS. 
The first or lowest till sheet consists of a fine textured and very com- 
pact clay in which there is a small amount of sand, numerous pebbles 
and small cobbles, derived chiefly from the underlying limestone, with a 
very much smaller number derived from the archean rocks. Scattered 
through the till there are frequently found larger boulders and_ blocks, 
~ usually of gneiss, granite, or some of the associated rocks ; occasionally 
large boulders of the Trenton limestone occur. The boulders appear to 
be segregated in different parts of the till, there being long stretches nearly 
free from them between the localities where they are particularly abund- 
ant. The sheet has nowhere been found to present the slightest trace 
of stratification, even in the thickest sections. Wherever the bed rock is 
_exposed this sheet is found to rest directly upon it. Its upper surface is 
undulating, so that at times it rises in dome-shaped hills above the sur- 
face of the lake, at times it lies below present water level. The maxi- 
mum thickness observed in the lake-shore sections here described is 
about fifty feet. 
The till of the second sheet, and of the two smaller sheets lying be- 
neath it (designated A and B in the section given above), is almost 
identical with that of the lowest sheet, except that it seems to be slightly 
more arenaceous, the pebbles are smaller and less numerous, and 
boulders are almost wanting. The sheets preserve a very uniform 
thickness throughout their extent, being thus in very marked contrast 
to the lowest sheet, whose upper and lower surfaces are both irregular. 
The writer is inclined to regard the two small intermediate sheets of 
till as marking temporary and local advances and retreats of the ice 
sheet by which the till of the second sheet was laid down. In the field 
the actual ends (in the lake-shore section) of neither of these sheets 
could be located, although it is possible to assign a maximum length. 
The evidence available does not warrant the conclusion that they were 
of much greater extent and were eroded before the deposition of the 
second till sheet or of the sands immediately beneath it. 
The uppermost, or third till sheet, differs much from any of the pre- 
ceding. In many places it consists of two distinct portions, a lower 
part closely resembling the till of the lower sheet, and an upper part 
with a well-developed bedded character, and composed of a loose, sandy 
till in which there is but a small amount of clay. In the field it was 
not found possible to map the two portions separately. In places the 
two are very intimately associated. The clay portion will occur in 
