32 THE NAOTILCS. 



now know as the Tennessee System, and the other in the southwest, 

 probably in the Ozark region. 



Assuming the origin of the Naiad fauna in the western region 

 above mentioned, the first question to be determined is the deriva- 

 tion of the Atlantic fauna from this primitive fauna of Cretaceous 

 time in the west. 



The oldest land in eastern North America is that known as the 

 Laurentian Highlands of Eastern Canada. With the gradual ele- 

 vation of the continent in early times, which ultimately resulted in 

 a connected land surface from the east to the mountainous regions of 

 the west, the earliest system of drainage that was established in the 

 region now occupied by the Great Lakes, was, according to the con- 

 sensus of the best geologic opinion, towards the west, and when, in 

 process of time, the highlands known as the Appalachian Mountains 

 and the Cumberland Plateau were raised up, they formed a water 

 shed, which determined the then existing systems of drainage. 



According to Branner (1), prior to Cretaceous times, the then 

 Cumberland Plateau extended continuously from the Appalachian 

 Mountains southwest into western Texas. At that time the Missis- 

 sippi River was riot in existence, the drainage from the south of this 

 great water shed was into the Gulf of Mexico, the drainage from its 

 north side was north and west, and probably in the beginning, ended 

 in the great Mesozoic sea, which extended along the foot of the 

 Rocky Mountains from the Gulf of Mexico to the Arctic Ocean. 



While we do not know as much of the exact course of these pre- 

 glacial rivers as we should like, nor as much as we hope to know in 

 future, there has been of recent years a considerable advance in our 

 knowledge in this particular, and there is enough of data now avail- 

 able to give us at least a general idea of some of the particulars of 

 that ancient drainage system. It was, of course, entirely over- 

 whelmed and nearly obliterated by the effect of the ice cap, which 

 overthrew the ancient system, and from which grew our present sys- 

 tem of drainage, but here and there there are enough remnants to 

 afford us some information as to the lines along which this pre- 

 glacial drainage system was established. 



As shown by Fig. 3, which is copied from Grabau (2), the pre- 

 glacial drainage of the region of the lower Great Lakes was towards 

 the southwest. The ancient Dundas River, originating in the Lau- 

 rentian Highlands, flowed southwesterly across the present bed of 



