ABSTRACTS 221 



outlet was at the foot or east end of Trout Lake about twelve miles 

 east of North Bay. The Nipissing beach though faint can be followed 

 to the foot of Trout Lake. 



The effects of the flowing current of the ancient outlet river are well 

 marked at several points. The places of several ancient rapids and one 

 cataract were found. The cataract was at the present Talon Chute and 

 the four most notable rai)ids were, (i) below Turtle Lake, (2) below a 

 lake called Pimisi Bay, (3) at the modern Des Epines Rapids and (4) 

 at Mattawa. The falls were 25 to 30 feet high and the postglacial 

 gorge made by them is very distinct. It is not quite half a mile long, 

 but it is deep and averages only about 300 feet in width. The walls 

 are of red granite and vertical 40 to 100 feet. A thin and highlv 

 inclined bed of crystalline limestone passing down into the gorge from 

 the west may have hastened the cutting somewhat. The ancient river 

 was expanded to a lake in the Lake Talon basin, and made faint but 

 distinct shore lines by wave action. One is 20 feet above the present 

 lake and the other ten or twelve feet higher. The mark of the surface 

 level of the river was quite plain at some of the rapids. On the north 

 side at Des Epines rapids this mark is 55 feet above the present river. 

 The channel at that level was between 600 and 700 feet wide and 

 averaged 35 to 40 feet in depth, and the current was strong enough to 

 move gravel and pebbles of small size. This corresponds in a general 

 way with the size of the modern St. Clair River. 



Ancient rapids were recognized in three ways. There are several 

 narrow passages that are heavily bowlder-paved. They mark the 

 points where moraines cross the channel. At Des Epines and Mat- 

 tawa the bowlders of gneiss and granite are worn and scoured into 

 many curious forms. Many were found with basins or potholes bored 

 in them and a few bored clear through so as to become ring-bowlders. 

 At each of these rapids a stream enters just above and furnished a con- 

 stant supply of gravel, sand and pebbles for the current to roll over 

 and among the bowlders. The rapids below Turtle Lake and Pimisi 

 Bay are of the same sort except that the water issued from lakes, and 

 so had no supply of gravel to scour with. The third way of recogniz- 

 ing rapids was by inference indirectly. Such rapids were in narrow 

 defiles or canyons with walls of bare rock and the fact that rapids had 

 existed there was inferred from the observed drop in the surface 

 level of the river above and below. The remains of the ancient Nipis- 

 sing- ]\Littawa River agree with the Nipissing beach in indicating that 



