140 



Scientific Geology. 



as the Deerfield and the Westfield pass, in the primary Tegions. 

 Masses of rock of various sizes, even 10, 15, or 20 feet in diameter, 

 may here be seen, some of them torn up from their beds and removed 

 a considerable distance, strewing the bottoms of the streams, and at 

 low water almost covering the surface ; and others, only partially 

 lifted from the parent rock, and waiting for another convulsive effort 

 of the torrent to detach them, and give them an erratic character. 

 In short, one sees in such streams a cause fully adequate to the pro- 

 duction of those numerous bowlder stones that are scattered over the 

 country : I mean, a cause sufficient to detach and round them. Prob- 

 ably, however, the expansive agency of water, frozen in the seams 

 of these rocks, contributes not a little to lift them ,out of their orig- 

 inal beds. 



Valleys of Denudation. 



When the strata of rocks on the opposite sides of a valley coin- 

 cide, the conclusion seems inevitable that they once formed a contin- 

 uous stratum, and that the valley has been subsequently excavated. 

 The appearance in such cases indicates that it has been scooped out 

 by running waters ; and yet, this might be the appearance if water 

 had only modified the sides and bottom of a fissure produced by other 

 causes. And in some cases, at least, it seems necessary to callinthe 

 aid of other causes. 



I am in doubt whether there is more than one valley in Massachu- 

 setts that is, strictly speaking, a valley of denudation. And that is 

 the passage between Mount Toby, in Sunderland, and Sugar Loaf 

 Mountain, on the opposite side of Connecticut river. I have already 

 described the appearance, and given a drawing of Sugar Loaf, and 

 the geologist will at once perceive it to be a remarkable outlier, rising 

 about 500 feet above the Connecticut, composed of red sandstone ; 

 whose strata dip to the east about 15°. On the opposite side of the 

 river are red sandstone strata, dipping in the same direction. Sugar 

 Loaf appears as if it had been modified by the action of water, even 

 to its summit ; and so on the opposite side of the river, I have al- 

 ready shown, in the second part of my Report, that Sunderland cave 

 may be accounted for, by the undermining operation of water upon 

 the softer strata. And the valley of the Connecticut above this point 

 exhibits none of those proofs that the river could not have excavated 

 it, which exists as to the valley in general, and which I have already 



