﻿I72 NEW YORK STATE MUSEUM 



were swept southward by the earlier glaciation. Later ice work 

 with more abrasive power planed the harder stratified rocks, grooved 

 the limestones, modified the topographic forms by softening the 

 scarps and rock knobs and straightening the drainage lines. One 

 or more long interglacial epochs partially restored the character- 

 istic atmospheric-erosion forms of the Theresa and Pamelia scarps 

 and cuesta fronts; reexcavated the valleys and basins; and de- 

 stroyed the surficial glaciation on the sandstones and limestones. 

 The latest ice sheet finding the northward region denuded of rock 

 debris and smoothed by the earlier glaciation was unable to arm 

 itself for effective erosion and thus handicapped was competent only 

 to weakly abrade in places. It is possible that while the deglacia- 

 tion interval in our district produced some weathering effects the 

 northward (Labrador) region was continuously snow-covered and 

 the ice was not able to pluck a new supply of granitic tools. 



Undoubtedly there were important differences in the behavior 

 and mechanical effects of the several ice sheets, due to differences 

 in rate of accumulation and velocity of flow ; of depth and pressure ; 

 of temperature and rate of waning; and these combined with, and 

 an effect of, climatic variations. 



It would have been entirely proper in this writing to have as 

 sumed multiple glaciation and confidently to have explained the 

 singular features of the area on that basis. Perhaps the method 

 of argumentation which has been used is somewhat confusing to 

 the reader, but he will better appreciate the complexities of the 

 study and its consequent fascination. 



ECONOMIC GEOLOGY^ 



While the district under consideration is bordered on the east 

 by an area in which hematite, pyrite, galena and talc have been, 

 or are being, mined, none of them have been found in anything 

 like workable quantity within the limits of the map. The fer- 

 ruginous quartz schists of the Grenville are present in quantity but 

 are very lean ores indeed. One mile north of Theresa on the Red 

 lake road a small opening has been made on a hematite mass which 

 occurred as a direct replacement of Grenville limestone. The ma- 

 terial was a finely crystalline, scaly, specular iron, and was of great 

 purity, but there were only a few tons of it. While therefore the 

 deposit was of interest as a clear and pretty example of replace- 

 ment of the sort, it had no economic value. 



*By H. P. Cushing. 



