GLACIO-AQUEOUS AGENCY IN NORTH AMERICA. 209 



who can doubt that the work is even now advancing ? And yet 

 it began during the glacio-aqueous period. 



10. Fractured Rocks. 



I have discovered three examples in which ledges of rocks have 

 been fractured at their top in such a manner, that it may reason- 

 ably be imputed to the agency of ice. One of these cases I found 

 upon the western rail-road, in the town of Middlefield. PI. VIII, 

 fig. 15, shows the appearance of an excavation for the road, while 

 yet it was in progress ; that is, it shows the sides and end of the 

 cut. The left hand side of the figure shows the south side of the 

 excavation, and the right hand the north side. The rock in place 

 is hornblende slate, whose strata stand perpendicular and run 

 nearly north and south. Above the rock is represented a deposit 

 of drift, about twenty feet thick. In the wall, crossing the excava- 

 tion, are seen several cracks, to the depth of eight or ten feet 

 below the surface of the rock, which are filled with mud and clay. 

 These result from some force which has fractured the ledge to that 

 depth, and bent the strata so as to make them incline towards the 

 south. Similar cracks show themselves in the side walls. In 

 short, the strata are broken off and pushed somewhat out of place, 

 by a mechanical force. Now I can only say, that it is easy to 

 conceive how such an effect might be the result of a thick mass 

 of ice resting on this ledge, and crowded, either by expansion, or 

 some other vis a terg-o, down the deep valley where this spot is 

 situated. But whether it was actually produced in that manner, 

 I have no other evidence to show. It must have required a pro- 

 digious force, pressing southerly, to produce the fractures ; and 

 such a force ice could exert ; and I hardly know of any other 

 agent that could do it. 



My second example is at Bruce's quaiTy of argillaceous slate, 

 in the east part of Guilford, in Vermont, near the stage road from 

 Greenfield to Brattleborough. The quarry is situated on the 

 western side of a hill, of perhaps two hundred feet in height, and 

 the laminae of slate here stand nearly perpendicular, leaning how- 

 ever a little to the east, and running nearly north and south. The 



