644 THE JOURNAL OF GEOLOGY. 
powerful streams have cut out picturesque ravines, such as are 
seen along the Don and Humber. 
It is probable that at the end of the first inter-glacial period the 
topography had almost as old an aspect as at present, indicating 
as long a time for erosion as has elapsed since the last ice age; 
but the dry land stage during the second inter-glacial period was 
apparently much shorter. The length of time during which high 
water lasted during the two mild periods must have been very 
great to allow the immense sedimentary beds to be deposited at 
Scarboro’ and elsewhere, 150 feet thick in the earlier period and 
160 in the later. The Iroquois high water stage after the last ice 
age was probably much shorter, since it has left much smaller 
sedimentary deposits. 
It is a notable fact that each ice-sheet advanced apparently 
during a time of low water, and was followed by a stage of high 
water; whether this is to be accounted for by assuming an ice 
dam at the foot of the predecessors of Lake Ontario, or a change 
in the level of the land surface caused by the loading and unload- 
ing of its ice burden, it is very unlikely that the sea has 
extended inland so far as Toronto since glacial times. The 
numerous marine animals found as fossils lower down on the St. 
Lawrence and Ottawa would hardly have stopped short without 
reaching the Iroquois bay, if that had been a body of salt water, 
in communication with the Gulf of St. Lawrence.* However, no 
fresh water forms have been found on its beach, so that the evi- 
dence is only negative. 
The Scarboro’ beds give very instructive evidence as to the 
comparatively slight erosive power of glaciers. Except near the 
east end of the section, where, as suggested to me some time 
ago by Mr. J. B. Tyrrell, the ice front began to rise upon the 
higher ground during the second advance and crumpled and con- 
torted the clay beds, there is no very striking disturbance even of 
the stratified sand, though here and there portions of the sand 
* Two marine shells have been picked up on the Iroquois beach, but, as suggested 
by Dr. Dall, to whom they were submitted, they have almost certainly reached that 
position by human agency. 
