W. J. Miller — Ice Movement and Erosion. 297 



are presented in the most favorable attitude for abrasion. The 

 wearing down would go on until the resisting rock front had 

 attained a height and weight sufficient to counterbalance those 

 of the glacier. " In the Black river valley the ice moved from 

 the crystallines against the slightly upturned edges of the sed- 

 iments. 



In much the same way the soft shales were stripped off the 

 surface of the hard limestones to form the broad terrace 

 and the steep front of Tug Hill. Such a stripping off of the 

 shales occurred, but to a less extent, over the southern part of 

 the Port Leyden quadrangle (except at Locust Grove; ; over 

 the northwestern part of the Boonville quadrangle; and over 

 the western part of the Pemsen quadrangle. This power of 

 erosion diminished southward. The maximum thickness of 

 shale thus removed was probably several hundred feet, but 

 not over a wide area. The total amount of shale removed 

 was not nearly as much as may at first sight be supposed. 

 Then, too, the shales were soft and highly jointed, even to a 

 considerable depth, as may now be seen in the Whetstone gulf 

 section. 



It may be fairly asked, what became of the materials thus 

 removed ? The very resistant Precambrians ought to be pres- 

 ent in considerable force as erratics somewhere in the region 

 and this is the case especially in the townships of Boonville and 

 Pemsen, where a vast number of such erratics may be seen 

 strewn over the country. Shale and limestone is also present 

 in great abundance in the till and other drift of the Pemsen 

 quadrangle. However, much of the shale must have been 

 ground up and carried away by glacial waters. 



Two other factors which greatly aided the work of the ice 

 in' the Tug Hill region must not be overlooked. One of these 

 is the fact that the ice moved up hill as it advanced southward 

 along the valley and so had its cutting power increased. On 

 reaching the divide between Black river and West Canada creek 

 the cutting power was lessened and till and other drift mate- 

 rials were deposited in great quantities as the ice moved down 

 hill toward the Mohawk river. Another factor which the 

 writer regards as important in this connection is the angle at 

 which the ice current entered the Black river valley in its 

 sweep around the Adirondacks. The greatest amount of 

 erosion was along the eastern side of Tug Hill, and it was just 

 here where the ice current must have struck with greatest force 

 as it was crowded into the valley. In harmony with this idea 

 is the fact that the glacial striae near Martinsburg bear more 

 towards the south than does the steep front of Tug Hill. 



It appears to the writer that, even under these favorable 

 circumstances, the ice did not show itself to be such a great 



