1882 .] 
361 
[Davis. 
The peculiar course of the Clyde or Seneca river, the common 
outlet of all these lakes, is also controlled by the moraine and not 
by the rocks below; its variations during and after the glacial 
period are probably like those described by Berendt for the 
Weichsel in North Germany. 1 The valley of the Genesee also 
presents certain features worth mentioning in this connection. 
Between Mt. Morris and Rochester, the river follows its pregla- 
cial valley, but flows for much of this distance on an alluvial 
plain that closely resembles the filling of an old lake ; above and 
below the limits named the river has cut a new channel since 
glacial times, giving some of the best natural sections in the state, 
and its old course is choked with drift. 2 In two particulars, then, 
the modern form of this old valley is unlike that of its fellows 
farther east : first, its headwaters have abandoned their old chan- 
nel and made a new one ; second, the lake that existed for a time 
in its middle course has been filled up. Evidently, therefore, the 
filling of the lake is the result of the cutting a new channel; 
one of the peculiarities of the modern Genesee depends on the 
other. 
West of Lake Winnipeg, a number of lakes stand in valleys 
of the “ third prairie” level, shut in by the “ Coteau”; they are 
saline, 3 but in other respects seem very similar to the above 
group. 
C. 4. Drift Barrier Ba ins. Besides the lakes of the previous 
species, whose barrier is entirely or in part referable to a terminal 
moraine, there are many others whose obstruction must be given 
the more general name of glacial or fluviatile drift ; it will doubt- 
less be possible with closer examination to recognize the special 
form in which the drift occurs, but as yet the subject has seldom 
received minute attention. 
The detritus of the glacial period was deposited with much 
irregularity and it must often have interrupted the drainage-lines 
of preglacial times ; we cannot doubt that the greater number of 
1 Deut. Geol. Gesell. Zft., xxxi, 1879, 14. 
2 Hull, Geol. Surv. N. Y., 4th Distr., 1843, 371, 422, gives some particulars of this 
region ; the clogging of the old outlet by Portage formed a lake there, which was 
drained by the new channel from Portage to Mount Morris. 
3 Dawson, Geol. Soc. Journ., xxxi, 1875, 615. 
