198 ILLINOIS STATE ACADEMY OF SCIENCE 



In the immediate neighborhood of Killarney, in the 

 village itself, one may see all but the last type of glaci- 

 ated rock hole. At the rocky point, at the west end of 

 the channel, on the north side of the water, one may see 

 the depressions formed by two types of giant chatter 

 marks. In the walk outside the MacDonald Hotel one 

 may see the depressions formed by the intersection of 

 joints, and by the conchoidal fracture of Killarney gran- 

 ite, and there are excellent illustrations of the way in 

 which the glacial abrasion truncated and partly de- 

 stroyed some depressions which had been made at an 

 earlier time. Only those which came in the later period 

 of glaciation are preserved intact. In a garden near the 

 store of Mr. T. Jackman there is a rock exposure which 

 shows admirably the way in which some of the pegma- 

 titic and miarolitic material in the granite weathers into 

 pitted shapes something like pot-holes. 



A significant argument that the pot-holes are indige- 

 nous to the granite and not the result of any outside 

 agency is the fact that the quartzites of the same district 

 contain almost no such depressions. Photographs show 

 the peculiar shape of the glaciated surfaces of the granite 

 rock moutonees. Almost all of these peculiarities are 

 due to a normal glaciated surface, which is convex up- 

 wards in the direction of glacial movement, truncating 

 a smooth surface which has been glaciated, although not 

 fashioned by glaciation, and which is concave upwards. 

 Some of these concave surfaces were in existence before 

 glaciation, some came into being during glaciation, and 

 others came after glaciation. (Figure 8.) 



Thus it is stupid to suppose that all concave surfaces, 

 or even holes, in glaciated rocks are due to the work of 

 subglacial streams. It is quite clear at Killarney that 

 several other agencies made such depressions, and there 

 is no evidence that any of these "pot-holes" were really 

 made by the spinning and swirling of boulders caught in 

 an eddy of a subglacial stream or at the bottom of a 

 moulin in a glacier. Striking as these holes are, they do 

 not seem to have been bored by any natural gimlet, such 

 as a spinning boulder in running water. Indeed, this 

 area provides the evidences of "pot-holes" of hitherto 

 undescribed methods of development. 



