182 



toward the north-east, and the latter toward the south-west. I 

 conceive, on the contrary, that when these different basins were 

 occupied by the sea, and the sediments which they now hold 

 were accumidating, the Narragansett basin, equally with the 

 other two, communicated with the Gulf of Maine, and had its 

 head toward the south-west, in the vicinity of Newport. The 

 oscillation which submerged the eastern border of the Gulf of 

 Maine, or some similar tilting of the land,^ has subsequently 

 brought about a change of level in this trough, so that what 

 was formerly its head is now open to the sea. The proofs of 

 this are : ( 1 . ) The crystalline Montalban strata appear to 

 pass on the south-west entirely around the uncrystalline sedi- 

 ments of this basin. (2.) The outcropping of the earlier 

 deposits in the basin from beneath the newer, as where tl5,e 

 rocks referred to the Shawmut group come up between the 

 granite and the Carboniferous beds on Newport Neck, is what 

 we shoidd expect at the head of a fiUed-up arm of the sea, but 

 not towards its mouth. Along the west side of Narrao-ansett 

 Bay, and farther north on the same line, there are slates and 

 conglomorates between the crystallines and the Carboniferous, 

 which differ widely from the latter, and are almost certainly 

 older, — possibly Devonian, as suggested by President Hitchcock. 

 (3.) If the drift were removed from eastern Plymouth County, 

 where it has a probable thickness, according to Hitchcock, of 

 three hundred feet, this part of the trough in question would 

 doubtless also be invaded by the sea, and, what is more to the 

 point, it would probably be observed that the Carboniferous 

 beds extend, in tliis direction, to and under Cape Cod Bay, 

 though they have never been so represented on a geological 

 map. 



It has been suggested that the strata occupying these basins 

 were once continuous over the intervening crystalline areas ; 

 the broad anticlinals having been removed by subsequent ero- 

 sion. I have seen no evidence of the correctness of this 



^The upturned Miocene beds on Martha's Vineyard are evidence of the existence of 

 eflBcient level-disturbing forces in this region, in comparatively recent geologic tiine. 



