232 Cincinnati Society of Natural History. 
the Laurentian mountains, and it is not improbable that earthquakes 
and volcanic energies had something to do with the emptying of these ~ 
vast bodies of water over the country to the south. The drift deposits, 
to the west of Lake Superior, which spread over part of Minnesota, 
and extend as far south as the Missouri river, belong to an overflow 
of the great central lake of British America, which is evidenced by 
the terraces and beaches of that extensive region. The overflows have, 
therefore, not only occurred ‘at different periods of time, but, probably, 
from three different bodies of water. Ifthen, all the phenomena are to be 
accounted for by ordinary and well known forces of nature, why call to 
their aid a glacial period, which will account for none of them. 
Taking a broad and general view, we would say that the drift 
upon the eastern part of the continent, from the mouth of the Hudson 
river to Hudson bay, is marine, and the strie upon the rocks were 
produced under water. The age dates back to the Pliocene era, and 
probably to the Miocene. When this margin was depressed, a corre- 
sponding elevation took place east of Lake Ontario, that blocked up 
the great river that had drained the central part of the continent, as 
far west as Lake Superior, during the Triassic, Jurassic, Cretaceous 
and earlier Tertiary periods. This elevation was more than 500 feet, as 
proven by the lacustrine clays exceeding that height, which were 
formed upon the hill and mountain ranges surrounding the great 
internal lake caused by this back-water, and as further evidenced by 
the fact, that after the lake had been permitted to stand at this height 
for so long a period as to form terraces and beaches, that later, it 
excavated the elevated barrier to a depth of 500 feet, forming a chan- 
nel, which is now in the bed of Lake Ontario, and when the eastern 
coast was again elevated, this region was correspondingly depressed. 
The drift on other parts of the continent is fresh water or lake drift, 
and the striae were produced, except in cases of drifting sand under 
atmospheric influences, by the action of water forcing harder materials 
against obstructions, or over barriers, and by floating shore ice having ~ 
frozen within it, the sand, gravel and bowlders of the place in which it was 
formed. In the Rocky mountain region, each valley is the limit ofits own 
drift phenomena; but when the northern part of the range was elevated, a 
very large interior lake was formed in British America, which seems 
to have covered many valleys, and in times comparatively recent, to 
have overflowed the country so as to empty itself in part, into the 
streams that flow south into the Missouri and Mississippi rivers. 
Another great overflow took place from the more central lake. 
Thiseam 
