508 GEOLOGY OF THE WESTERN DISTRICTS OF CANADA. 
one hundred feet beneath the general surface, and along the shores of 
Lake Erie and elsewhere forming hills one hundred and fifty feet 
above the general level,) is due to what is called by geologists the 
glacial period, and the phenomena referable to this epoch, are precisely 
similar on both sides of the Atlantic. From well known cosmical 
laws, ice-bergs and fields of floating ice are constantly, in seas north of 
the fortieth parallel of latitude, passing from the Polar regions in a 
direction from N.E. to §.W. and are conveyed for hundreds of miles 
from their original birth-places ; and these are frequently found to be 
charged with vast quantities of mud, sand and boulders, the debris of 
the granitic rocks which mostly occupy these regions. These ice- 
islands become stranded in seas too shallow to float them, and as the 
ice is melted, deposit their insoluble contents at random over the 
bottom of such seas, and the deposits thus formed would be stratified 
or unstratified according as the water was in a quiescent state or dis- 
turbed by currents. The slow passage of these ponderous masses, 
armed with such refractory materials, over the rocks forming the 
bottom of the seas, would grind down their upper surfaces, removing 
great quantities of their constituent materials, and producing grooves, 
furrows and scratches in the normal direction of their course. We 
have, on a small seale, an example near our own doors of the effect of 
ice in removing masses of rock. I refer to the fact that the isolated 
rock called Gull Island, between Cobourg and Port Hope, two miles 
from the northern shore of the lake, and on which the lighthouse is 
built, formed at the time of the early settlement of the country, an 
island of over two acres in extent, but is now only a sunken reef, 
owing doubtless to its having been as it were decapitated by the ice 
forming over and adhering firmly to its upper beds, which would be 
borne away with the floating ice during storms. The same process is 
continually going on upon a larger scale in Lake Superior, and the 
observations of navigators in the Arctic regions supply, on a still more 
extensive scale, all the “ modern instances” requisite for the corrobora- 
tion of the theory. 
Now it is an interesting and important fact that the constituent 
materials of the clay, sand and gravel which cover the greater part of 
Canada West, are derived from granitic and trappean rocks ; that the 
boulders embedded in the clay and strewed over the surface are, for 
the most part, fragments of the same rocks; that these rocks are found 
in their native beds invariably in a North-easterly direction, and that 
