422 Scientific Geology. 



at no great distance in the valley, having such a dip as would cause 

 it to rise above the greenstone. I hence infer, that originally, nearly 

 all the greenstone was interposed between the strata of sandstone ; 

 and that subsequent abrasion has removed the latter rock. Even in 

 those cases where we find insulated masses of the trap lying upon 

 the sandstone, there is reason for supposing that it is the wreck of 

 one of these interposed masses ; disintegration and abrasion having 

 effected the destruction of the other portions of both the rocks. 



At Turner's Falls, Connecticut river has disclosed, between Mon- 

 tague and Gill, an interesting section across the sandstone and green- 

 stone, not less than three miles long. In the 6th Vol. of the Am. 

 Journal of Science, I inserted a very detailed view of this section : 

 but having examined it recently with more care, I shall give a cor- 

 rected sketch ; which, though less particular, will I trust be found 

 more accurate and instructive. It commences on the western side of 

 the greenstone ridge against which Connecticut river impinges, a 

 little below Turner's Falls, and by which its course is changed from 

 northwest to south. At the western base of this ridge, the sandstone 

 crops out beneath the greenstone, dipping perhaps 20 or 25 east. 

 After passing easterly over this ridge, we find at the mouth of Fall 

 River, another variety of the sandstone, mounting upon the green- 

 stone at an angle of about 45; that is, dipping easterly by that quan- 

 tity, and running nearly north and south. Proceeding in the same 

 direction, the sandstone continues only a few rods, perhaps 15, when 

 we find it on the north shore of Connecticut river passing under an- 

 other ridge of greenstone, 15 or 20 rods thick. On the east side 

 of this second ridge, we find a similar variety of slaty sandstone dip- 

 ping about 50 east. Several varieties of sandstone, some red, some 

 gray, some fined grained, and some coarse grained, appear, as we pass 

 along the same shore, with a dip between 40 and 50 east, for more 

 than a mile. There we strike a somewhat more elevated ridge, 

 which appears on both banks of the river, consisting of a brecciated 

 indurated sandstone, described among the varieties of new red sand- 

 stone, whose strata are somewhat saddle shaped on the north shore, 

 though quite indistinct. Beyond this point the shores for some dis- 

 tance are less bold, and no rock is visible for half a mile. When it 

 again appears, the direction of the strata becomes nearly east and west, 

 and the dip from 30 to 40 south. Hence only the horizontal edges 

 of the strata can be shown on the section. But when we come with- 

 in 100 rods of the mouth of Miller's river, the sandstone slate or 



