50 NEW YORK STATE MUSEUM 



BelP has noted similar conditions in Canada and he says that when 

 the ice sheet moved from the crystallines against the edges of the 

 unaltered sedimentaries "great erosion has always taken place and 

 valleys and basins are formed whose width depends upon the angle 

 of dip and the softness of the strata which have been scooped out. 

 The strata are presented in the most favorable attitude for abrasion. 

 The wearing down would go on till the resisting rock front had 

 attained a hight and weight sufficient to counterbalance those of the 

 glacier." In the Black river valley the ice moved from the crystal- 

 lines against the slightly upturned edges of the sediments. 



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

 face 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 quad- 

 rangle and the western part of the Remsen quadrangle. The maxi- 

 mum thickness of shale thus removed was probably several hun- 

 dred feet, but not over a wide area. The total amount of shale re- 

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

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

 able depth as may now be seen in the Whetstone gulf section. 



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 be- 

 tween Black river and West Canada creek the cutting power was 

 lessened and 'till and other drift materials 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 con- 

 nection is the angle at which the ice current entered the Black river 

 valley in its sweep around the Adirondaeks. The greatest amount 

 of erosion was along- the eastern side of Tug hill, and it is just here 

 where the ice current must have struck w^ith greatest force as it 

 cT-owded into the valley. In harmony with this idea is the fact that 

 the glacial striae near Martinsburg bear more toward the south than 

 does the steep front of Tug hill. 



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

 moved? The very resistent Precambrics ought to be present in 

 considerable force somewhere in the region as erratics and this 

 is the case southward especially in the townships of Boonville and 

 Remsen where vast numbers of such erratics may be seen. Shale 



Geol. Soc. Am. Bui. 1890. 1:296. 



