50 
ORIGIN OF LIFE IN AMERICA 
Other species of fishes related to marine forms live in the 
Great Lakes. But we need not suppose that typical fresh¬ 
water fishes are absent. The family of Cyprinids, those 
essentially fresh-water fishes to which the carp belongs, is 
well represented there. Hence if we suppose that they were 
destroyed during the invasion of that region by the sea, the 
lakes must, at a subsequent period, have been freely connected 
with rivers which were stocked with fresh-water fish. And 
it appears that this actually has been the case. 
Whether the St. Lawrence was choked by obstructing ice 
masses, or whether it was filled with detrital matter carried 
down from the neighbouring eastern heights, does not affect 
our present inquiries. It seems that after the ice, or, if we 
prefer it, after the retreating sea, had left the district, there 
were only three lakes instead of the five as at present. These 
three lakes, which have been called “ Duluth,” “ Chicago ” 
and “Maumee,” were independent of one another. Lake 
Duluth emptied its waters into the Mississippi, Lake Chicago 
excavated an outlet which has since become the Chicago 
drainage canal, while Lake Maumee communicated with the 
Wabash River. All, of course, eventually helped to swell the 
waters of the Mississippi. Lake Maumee gradually developed 
into the huge Lake Warren. Later on the other lakes joined, 
and poured their waters into Ontario, which then communi¬ 
cated with the Hudson by means of the Mohawk River. It 
was only then that the sea finally broke down the barrier* 
which had prevented an overflow into the St. Lawrence, and 
advanced as far as the western end of Lake Ontario, one 
marine channel communicating with the Atlantic by way 
of the Hudson Valley. 
We can easily imagine how the fresh-water fishes of the 
north, which were either killed or driven south, such as the 
redfin (Notropis cornutus) and Notropis atherinoides (it does 
not seem to possess a common name) managed to return to 
their northern stations after the Glacial Epoch. Yet I feel 
sure that a survival even of some fresh-water fishes took place 
within the drift area in some of the eastern mountain ranges. 
Near Freeport in Maine, quite an isolated colony of the 
beautiful red-bellied dace (Chrosomus erythrogaster) occurs. 
This is probably a pre-Glacial relict. Nor is it likely that 
