Great Zakes, and the Valley of the Mississippi. 217 



venture still further, and predict the discovery of buried chan- 

 nels of communication between Lake Superior and Lake Michi- 

 gan — probably somewhere near and east of the Grand Sable — 

 at least, between the Pictured Rocks and the St. Mary's River — 

 between Lake Erie and Lake Ontario through Canada, — be- 

 tween Lake Ontario * and the Hudson by the valley of the Mo- 

 hawk, — between Lake Michigan and the Mississippi, somewhere 

 along the line I have before indicated. I also regard it prob- 

 able that a channel may be found connecting the upper and 

 lower portions of the Tennessee River, passing around the 

 Mussel Shoals. This locality lies outside of the area where the 

 Northern Drift deposits were laid down to fill and conceal 

 ancient channels, but the excavation and the filling up of the 

 channel of the Tennessee — like that of the Ohio — were deter- 

 mined by the relative altitude of the waters of the Gulf. The 

 channel of the Lower Tennessee must have been excavated 

 when the southern portion of the Mississippi valley was higher 

 above the Gulf level than now, and Prof. Hi 1 gar d has shown 

 that at a subsequent period, probably during the Champlain 

 epoch, the Gulf coast was depressed 500 feet below its present 

 relative level. This depression must have made the Lower 

 Mississippi an arm of the se'a, by which the flow of the Ohio 

 and Tennessee was arrested, their channels filled, terraces 

 formed, &c. If the Upper Tennessee has, as appears, a channel 



* When the water in the lake basin had subsided to near its present level 

 old avenues of escape being all silted up by the Drift clays and Bands, the Burplui 

 made its exit by the line of lowest levels wherever that chanced to run. A.- thai 

 happened to lie over the rocky point that projected from the northern extremity 

 of the AUeghanies into the lake basin, there the line of drainage was established 

 in what is now known as Niagara river. 



Though among the most recent of the events recorded in our surface genii 

 this choice of the Niagara outlet by the lake waters was made so long ago thai all 

 the erosion of the gorge below the falls has been accomplished since. The 

 cavation of the basin into which the Niagara flows— the basin of Lake Ontario, 

 of which Queeustown Heights form part of the margin— belongs lo an epoch long 

 anterior. 



