3/6 The American Geologist. J""'^' ^'^'^'^^ 
oscillations were several times repeated, so that the Pleistocene 
period was composed of several glacial epochs separated by in- 
terglacial epochs. Each interglacial epoch had its own system 
of lakes and rivers, and in one of these epochs a great river 
traversed the Niagara district, crossing the escarpment a few 
miles west of the mouth of the Niagara gorge. Like the Ni- 
agara, it made a gorge, and this gorge was eaten back from 
the neighborhood of the village of St. Davids to the position 
of the present Whirlpool. The readvance of the glacier not 
only abolished this river but filled with drift the gorge it had 
made, so that one may now cross it on what is known as the 
Old Portage road without suspecting the existence of a buried 
valley. 
"When the ice for the last time melted from the land, it 
left a hollow which we laiow as the basin of lake Erie, and 
another hollow which contains lake Ontario, and it left the face 
of the land in such shape that the overflow from one lake to 
the other could not follow the valley of an earlier stream but 
sought out a new course. Thus the Niagara river was born ; 
and its cataract has been engaged ever since in the making of 
the gorge. 
"Just before the establishment of lake Ontario there was a 
greater lake in the same basin, with an outlet to the Mohawk 
and Hudson rivers instead of the St. Lawrence. The aban- 
doned shore of this greater lake, called by geologists the Iro- 
quois beach, lies close to the escarpment and can be traced out 
bv means of its bluffs and ridges. Its line is followed for 
many miles in New York by a road called the Ridge road, and 
this road crosses the map. At Dickersonville it runs on a typ- 
ical beach ridge of gravel and sand. Near Model City it is 
on top of the ancient shore bluff, and in Lewiston it is on a 
gravel ridge which was built as a spit in the old lake. 
"After the disappearance of the ice the land it had covered 
was gradually uplifted, the rate of rising being different in dif- 
ferent parts. As a result of this warping of the earth the out- 
lets of certain lakes were changed, and these changes had an 
important influence on Niagara river. There were two epochs 
during which most of the water of the great lakes region 
flowed to the ocean by other routes, leaving to the Niagara only 
the water from the lake Erie basin. During these epochs the 
river was much smaller than it now is, probably carrying only 
