EXAMPLES OF EROSION. 87 



nati. It proceeds on the supposition that the Appalachian and Illinois coal fields 

 ■were once continuous. In that case, the strata at Cincinnati must have been swept 

 off to the depth of about 2000 feet. Plate XII, Fig. 3, copied mainly from Lyell's 

 Travels in the United States, will give an idea of this example. Prof. Locke had 

 promised me a more accurate statement of this case, but his recent death has deprived 

 me of this expected aid. I regret it, because I am aware that some geologists do 

 not place much confidence in this example, as indicating the amount of erosion, 

 and I feel myself unable to form a very decided opinion concerning it. It has 

 every appearance of a plain case, if we can judge from the figure, and Prof. Locke 

 felt quite confident of its reliability. 



I will venture to refer to one other example, which, in my estimation, will give 

 some approximate idea of the amount of this work of erosion. It is the part of 

 the Connecticut valley occupied by secondary rocks, especially the part reaching 

 from New Haven to Mettawampe, in Sunderland. It will be seen by Plate III, 

 that this valley is traversed by a few narrow and precipitous ridges, which consist 

 of trap based on sandstone, or rather interposed between its strata, as enormous 

 dykes or beds. Mettawampe and Sugar Loaf, however, are sandstone, and the 

 former rises higher than any mountain of secondary rock in the valley, being 1175 

 feet above Connecticut river, and 1295 above the ocean. Sugar Loaf is about 500 

 feet above the river. Plate XII, Fig. 2 is a section crossing the whole valley at this 

 place, from the gneissoid rock of Leverett on the east, to the highly inclined strata 

 of mica slate in the west part of Deerfield. The sandstone, dipping easterly from 

 5° to 30°, has an unknown depth, and rises to the top of Mettawampe. In passing 

 up the valley from Long Island Sound, this mountain and Sugar Loaf, which is 

 the southern termination of a ridge running north through Deerfield, Greenfield, 

 and Gill, are the first high bluffs of sandstone without trap, with which we meet, 

 and they stand up with almost perpendicular walls, having every appearance of 

 being merely the remnants of a formation that once filled the valley. There is no 

 appearance of any dislocation of the strata, although there does exist, near the 

 base of Mettawampe, a narrow bed of trap, as shown on the section. The valleys 

 east and west (right and left on the section) of Sugar Loaf, exhibit every appear- 

 ance of having been worn out by water, and it is difficult to avoid the conclusion 

 that the sandstone, at least to the height of Mettawampe, once filled the valley of 

 the Connecticut to Long Island Sound; a distance of, nearly 100 miles; and that 

 long exposure to oceanic action has worn the whole away as far as Mettawampe, 

 except where protected by the overlying trap. This latter rock, being excessively 

 hard, has in a great measure resisted these agencies, and now stands out in ridges, 

 whose rounded and furrowed surface indicates long continued powerful erosion. I 

 can assign no possible reason why these trap ridges thus remain, except that the 

 softer sandstone has been worn away, nor can I imagine any other agency which 

 could have accomplished the work, save the ocean. Judging from its effects in 

 other parts of the world, it is not extravagant to conclude that this is sufficient for 

 the mighty work. Nay, the probability is, that even Mettawampe shows us by 

 no means the original elevation of the sandstone. It may have been far greater; 



