Ponve.J 32 [February 6, 



Dr. T. S terry Hunt, to whose view I am glad to acknowledge 

 my indebtedness for much information of a general character 

 which in this paper I apply to local phenomena, when speaking 

 of the decomposition of the rocks referred to, uses the following 

 language : — 



" This change has affected the crystalline rocks of the southern 

 United States and of Brazil to the depth of a hundred feet or 

 more, and doubtless extended to all such rocks as were above the 

 surface of the ocean. The absence of this decayed material from 

 certain regions of crystalline rocks is to be attributed to its sub- 

 sequent removal by denudation, a process which in the northern 

 parts of Europe and America terminated at the close of the Plio- 

 cene period, when the remaining softened material was swept 

 away by the action of the water and ice, and the hard unchanged 

 rocks beneath were exposed and glaciated, since which time the 

 chemical decomposition of the surface hss been insignificant." 



In these words of Dr. Hunt there are two points upon which I 

 wish to comment, because of their bearing upon what I have to 

 say. One is that in relation to the depth of the disintegrated 

 rock material. This is found to be in the region mentioned by 

 him 100 feet or more in thickness. Now I am sure that neither 

 Dr. Hunt himself or any one else will think that this expresses 

 any adequate idea of the \ robable extent of the disintegrating 

 action, for there were undoubtedly in after ages when such action 

 had largely ceased to operate, influences at work to gradually 

 lessen the thickness of the deposit. In truth no one can venture 

 to say that it may not have been many hundreds of feet thick. 



The other point is Dr. Hunt's remark that since "the hard un- 

 changed rocks beneath were exposed and glaciated the chemical 

 decomposition of the surface has been insignificant. ,, 



This I wish to intensify by calling attention to the fact that 

 everywhere upon the hard rocks of New England the grooving 

 of the ice period may be distinctly seen, the action of the ele- 

 ments through the nges since they were made, not having sufficied 

 to obliterate them. 



There is yet an important general phenomenon to allude to 

 before making application of what has been expressed to the main 

 matter under consideration, and that is, the almost universal 

 exemption of portions of the material of the rock formations that 



