of Western Canada. 438 
§ 2. Deductions. 
The following deductions appear to flow naturally from the 
observations recorded above :— 
1. A general depression of the land, at the commencement of 
the Drift period, must have taken place to such an extent as to 
admit of the deposition of the lower clays. These latter were 
evidently derived from the limestones and other Silurian and 
Devonian strata lying beneath and around them. Hence their 
generally calcareous nature. Their derivation from this source 
is proved, moreover, by the pebbles of Trenton limestone and 
other fossiliferous rocks which they frequently contain. Exten- 
sive denudation must thus have occurred both immediately prior 
to and during the deposition of these clays; but it may be 
questioned whether the bolder contours offered by the denuded 
rocks, such as the escarpment that sweeps from the Niagara 
river to Cabot’s Head on Lake Huron, were not produced during 
the first uprise of the palzeozoic strata from the earlier seas in 
which their materials were accumulated, ages before the period 
now under discussion. It appears, at least, to be a well-admitted 
point, that these rocks had been elevated into dry land before 
the deposition of the higher formations in the south and west. 
2. After the deposition of the lower Drift clays, a sudden and. 
abrupt change in the character of the sediments took place. A 
striking example of this may be seen in the natural sections 
about Hoge’s Hollow, a few miles north of Toronto. The 
change in question must have been effected by a still further de- 
pression of the country, bringing the higher lands and gneissoid 
strata of the north within the influence of the waves, and yielding 
the sands, gravels, and boulders of the upper Drift accumulations. 
This depression permitted an invasion and broad extension 
southwards of the ice-covered Arctic seas, the trve cause, in all 
probability, of the cold of this epoch. ‘The depression must have 
exceeded 1500 feet, since northern boulders are found at that 
height above the sea on the Collingwood escarpment. The 
eneissoid boulders there met with must at least have traversed 
the basin of Georgian Bay; but the glacial strize which also occur 
there may have been produced by the action of ice origina- 
ting at the spot itself: the three or four distinct sets of strize 
observed at this locality, however, do not radiate from any fixed 
point, but run in the usual north and sonth direction, some being 
a little east and others a little west of north*. 
3. At the close of this second series of phenomena, a gradual 
* On a visit to this spot, since the publication of the “ Note on the Geo- 
logy of the Blue Mountain Escarpment” in the ‘Canadian Journal,’ vol. v. 
p. 304, some additional sets of striz were observed. 
Phil, Mag.8. 4. Vol. 21. No, 142. June 1861. our 
