76 The American Geologist. February, 1902. 
imagines the edge of the ice as close at hand on the northeast, 
so that its drainage could bring glacial sand and clay to the 
delta, while streams from,the westward contributed driftwood, 
leaves and mosses. 
There are thick beds of stratified glacial clays, lying be- 
tween two sheets of boulder clay belonging to the upper glacial 
deposits, which resemble somewhat the peaty interglacial 
clays; but when carefully studied the resemblance turns out 
to be only superficial. The glacial stratified clay contains no 
mica flakes, nor fossils, is charged with so much lime as to 
burn to a gray brick, for which it is largely used, and general- 
ly has a few angular pebbles, polished and scratched by ice ac- 
tion. The upper foot or two of these glacial clays has been 
weathered, however, and has had so much of its lime leached 
out by surface waters as to burn to a red brick. 
The interglacial stratified clays wherever found, at Séar- 
boro’ é6r the Don valley, show quite different characters. They 
always contain more or less of the peaty material usually asso- 
ciated with silty layers, charged with many greatly weathered 
mica flakes. Sheets of impure siderite are found as a rule every 
three or four feet. The clay contains much less lime than the 
glacial clays, and burns to a deep red brick. It is evident 
that the interglacial clay, if derived from the boulder clay or 
its associated calcareous stratified clay, has lost part of its lime 
and been enriched in iron. The small glaciated pebbles of 
glacial clays are entirely wanting, and in fact the upper lay- 
ers of peaty clay seem to be absolutely free from pebbles of 
any kind, though the lower ones, not far above the warm cli- 
mate sand and gravel, contain a very few well rounded stones 
and pebbles. 
The absence of evidences of glacial action and the fact 
that the interglacial clays are richer in iron and poorer in 
lime shows that they could not have been derived directly from 
the ice front a few miles away, but must have undergone a 
long weathering before being transported to the delta; and the 
wide spread thin sheets of siderite and of silty stuff contain- 
ing peaty fragments afford clear proof that the deposits were 
not made on a land surface, but in a wide and deep lake. These 
delta materials are known to cover more than 100 square miles 
to an average depth of from 50 to 75 feet, and they are prob- 
