172 THE PHETNOMENA OF DRIFT, OR 



of \hc road. I have noticed, also, a good example connected 

 with stria*, on the argillaceons slate at the quarry in Harvard, Mass., 

 and a still better one on the same roek in the east part of Guilford 

 in Vermont, where this rock is as nearly polished as its nature 

 admits. In all cases, however, these polished surfaces contain 

 more or less of stria?. 



When these abrasions appear on ledges facing the northwest, 

 that side of the rock is more or less rounded, and in many cases, 

 where portions of the rock rise above the general surface, a similar 

 appearance exists, which I shall describe more particularly further 

 on. But in general, the producing cause seems to have acted like 

 a huge plane, sweeping off the salient parts of the rock, and 

 leaving the hollows mostly untouched. And this is one of the 

 marks by which this agency is strikingly distinguished from the 

 action of mere currents of water. I will here refer to a well- 

 known locality, where the effects of these two agencies may be 

 seen in close juxtaposition. It is Bellows FeiUs, in Connecticut 

 river, bet^veen New Hampshire and Vermont, especially on the 

 Vermont side. The hard gneissoid rock at this place, shows on 

 its surface many distinct examples of the smoothing and striae 

 above described, while the sides of the deep gorge, which the 

 river has formed through the ledge, present no less striking 

 examples of such aqueous agency as is now in operation on the 

 globe. The first-named agency, which I call glacio-aqueous, 

 seems to have operated like a large heavy body, armed on its 

 bottom with gravers, driven along the surface with a prodigious 

 force, grinding down the prominences, but not conforming to the 

 sinuosities. On the other liand, the running water has produced 

 almost every possible variety of cm-ved surface in the rocks, which 

 are smoothed almost to a polish, but rarely if ever distinctly 

 striated. Close to the western extremity of the bridge over Con- 

 necticut river at this spot, may be noticed some rocks rounded 

 and striated by glacio-aqueous agency ; and the contrast between 

 this and mere aqueous agency may here easily be noticed. In 

 PI. VIII, f. 2, I have given a sketch of these rounded and striated 

 rocks, not because it is a very striking example, but because it 

 is so easily found by the traveller. 



