GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 177 



entire agency has been begun and ended since the deposition of 

 the tertiary rocks ? Where is the evidence that it commenced 

 earlier ? The direction taken by the bowlders, corresponding 

 with that of the stiise, and the almost equal freshness exhibited 

 by all the phenomena, lead to the conviction that the work was 

 one ; and that the period occupied by it was by no means one 

 of the longest of those which geology discloses : though there 

 is evidence that it was much longer than has been usually 

 supposed. 



I know of nothing that impresses the mind so much mth the 

 recency of glacio-aqueous agency, as a view of a surface of rock 

 smoothed and striated, which has been recently denuded of soil. 

 If other facts justified the conclusion, it would be easy, I think, 

 to satisfy one's self that these markings had been made within 

 the last two hundred years. If any one doubts this, let him com- 

 pare them with the letters upon the monuments in our church- 

 yards, placed there soon after the settlement of this country ; and 

 I am sure he will sometimes find the former the most distinct. 

 And yet, every geologist knows full well that the natural strisB 

 must have been made long before the creation of man. 



On the syenite of Rowley, in Massachusetts, I noticed a fact 

 that still more deeply impressed me with the recency of glacio- 

 aqueous agency. The surface was distinctly striated ; but on one 

 part it was scaling off to the depth of half an inch, and this ob- 

 literated all traces of the striae. Can it be that many thousand 

 years would be requisite to disintegrate the entire surface of 

 rocks to a depth so small ? And yet, wherever covered by soil, 

 the work seems hardly commenced. 



It is an interesting inquiry in what mode this smoothing and 

 furrowing of the rocks at all altitudes can have been accom- 

 plished. One supposition is, that the present inequalities of 

 surface did not exist when the work was done, and that the 

 mountains have since been elevated. This theory may satisfy 

 the closet geologist, but insuperable objections present them- 

 selves to him who carefully examines the localities. He will find 

 that the bowlders are deposited around and upon the mountains, 

 just as they would be, if those mountains existed previous to the 



