PROCEEDINGS OF SCIENTIFIC SOCIETIES. 499 



eal epoch; every contemporaneous formation being found in the 
AR regions of the south-west higher than to the north-east. 
g the glacial period, then, all the water-courses of the Upper 
issippi region were westward, and not southward as now. Not only 
Slope of the land, but the great folds of the Silurian strata compelled i 
ean conceive how it must have been cut up by ravines and valleys en- 
croaching on each other in endless confusion n, as we ow see in the bad 
t 
e whole Upper Mississippi region was the scene of the drift 
_ Action, and the valleys of preéxisting rivers were filled up and mostly 
buried out of sight. The existence of a distinct glacial moraine at War- 
ou on the Mississippi, shows that the glaciers were at least that far 
He had dsterininea the south-western limit of the glacial or drift action 
© be the pom river, from about the 48th down to the 43d parallel of 
et mo d s i 
for fifty miles east of their bases. The existence of this space 
the Missouri river and the Rocky Mountains shows that the form 
the Continent and seas in the glacial time were such as to produce in 
‘the climate relations similar to what now exist: namely, that the mountain 
acial mass must have been along the line of least 
°, and towards this limiting line, and the glacial scratches in the 
Mississippi region show that the motion was south-west. There, 
n that limit a river must have formed, to carry away the melting 
