252 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



Water must have passed over as a strong current, the place, where 

 the potholes are now but in their first stages only a slight depression 

 was in the rock. In these some hard stones collected and according 

 to the strength of the current, the movement of the stones would 

 depend ; the motion produced would soon lead to a wearing away of 

 the rock. Holes would form and deepen, as time rolled on, until a 

 cavity would be produced not unlike a pot in outline. In all the 

 holes examined, the diameter midway down was greater than at any 

 other point. The stones grinding this out being harder than the rock, 

 for you usually find they are pretty much the same as our boulders 

 in the field withstand the wear and tear well, but in the coui'se of 

 time they become rounded and finally succeeded in making a pothole, 

 which will vary in size according to the length of time the grinding 

 has continued, the force of the current and the hardness of the rock 

 acted upon. To-day we see no water near some of these holes, but 

 we find that when the loose soil in the bottom of the holes is dug up 

 it contains innumerable rounded stones of all sizes fi-om a marble to 

 that of a cannon ball. 



I have already said the mechanical action of stones and water upon 

 the limestone, in which we find these holes, has eflfected the condition 

 of things we at present observe. There are two ways in which these 

 currents of water may have acted. 



► 4. — Theories of Phenomena. 



1. That of a great river, which filled the whole space ))etween the 

 highest banks at Rockwood, a stream bearing along a great body of 

 water, with a strong current. As time rolled on it gradually lessen" 

 ed in volume and formed two streams, running along the valleys in 

 which we find the streams of to-day, but much larger than they. At 

 some period in this great river's existence it flowed across the 

 depression, where you see the largest Pothole, and flowing over the 

 precipice pursued its course along the line in which we find the other 

 Potholes. 



2. The water may have been a current under a glacier as we see 

 in some cases at the present time in Alpine districts. A crevasse 

 (crack) may occur miles from the end of a glacier, into this water 

 formed on the surface, as it pushes its way into warmer localities, 

 falls and finally makes its way out under the great stream of ice. 



