SIXTH REPORT OF THE DIRECTOR I909 189 



to do with the erosion of the '.arger features here shown. The 

 large chamber of Darkroom cave shows the same type of cutting 

 by falling and whirling waters carrying abrasive material. No 

 water whatever now enters the upper portion of this chamber. An 

 examination of plate 2.2 will show that the descending streams 

 which must have done this work were reflected and thus turned 

 from one place to another either along the fissure plane or from 

 one wall to its opposite. The shallow nature of the cut at (c) and 

 the deeper cuts at the right of it and below it are due to such 

 reflections of the falling stream. These caves present many 

 other examples of the same nature and the evidence, in all its 

 varied features, is wholly against any such cutting at the present 

 time and wholly for a cutting which must have taken place many 

 thousands of years ago. All of the cuts and the great chamber 

 in Darkroom cave with its horizontal and cylindrical outlet, 

 point irresistibly to the conclusion that we are here dealing with 

 glacial moulins cut in older rock fissures. 



This conclusion however opens up another field of great interest. 

 At the time of the melting of the later Wisconsin ice sheet the 

 rocks of Valcour island had been so far depressed by isostasy as 

 to bring their highest portions below the level of the sea. If the 

 caves had been modified by glacial drainage at that time, the waters 

 passing through these caves must have completely filled every por- 

 tion of them and been moved under great pressure. The leaping 

 of such a drainage stream from side to side, cutting now more in 

 this place and again in that (and cutting as if falling freely) 

 would be out of the question. The effects could not have been so 

 markedly localized as we now find them to be ; but would have been 

 of a larger and more uniform type. In order to find conditions 

 that would yield the effects we have here noted we are compelled 

 to go back to a time when the land was at least as high as it is at 

 present. It is quite possible that we have in these cases a witness 

 of moulin action at least as old as the earlier Wisconsin stage, if 

 \ not older. 



The next new item of proof offered by Bridge cave comes from 

 an examination of its northward extension. The entire cave roof 

 (the wedge between the two fissures) has been thrust down and 

 fractured, as the result of great pressure above. A depression 

 on the surface of the ground over the cave can be seen to run 

 many meters to the north although now covered with soil and 

 overgrown by trees and bushes. The only agent that could have 

 forcefully thrust down this wedge is glacial ice. 



