EESULTS OF THE ACTION OP OROGEMO FORGES. 23 



complete. In fact, it can not be believed that there was any distinct rela- 

 tion between these two movements — that of general downsinking and that 

 of warping nnder the inflnence of the lateral thrusting. 



It may be noted that the conditions of mountain building in this basin 

 resemble in a general way those of the Appalachian district, with the excep- 

 tion that in the latter region the neutral axis appears to have been in the 

 line of the ancient belt of the Blue Eidge or its equivalent ranges to the 

 north and south. Against this central ridge the thrusts apparently came 

 from the east and west. Moreover, in this Appalachian field the com- 

 pressive action seems to have been distributed over a much wider section, 

 with the result that the amount of deformation per unit of length in an 

 east-west direction was much less than was the case in the Narragansett 

 Basin. The folds are, on the average, less ci^owded together, and the 

 synclines are wider; in other words, the evidence goes to show that, in 

 proportion to the size of the disturbed area, much more movement was 

 taken up in folds in the Narragansett Basin than was the case in any part 

 of the West Appalachian field of disturbances. 



The relation of the mountain-building work of the Narragansett Basin 

 to similar action in the neighboring fields is a matter of much interest 

 There are three of these areas that deserve special notice — the Connecticut 

 Valley, Marthas Vineyard, and Boston Basin. Of these three regions of 

 mountain-building action, the one most remote — the Connecticut — ^is in all 

 respects the most unlike the Narragansett Basin in its orographic features. 

 In the Connecticut Basin we have what appear to be the same general 

 antecedent features noted in the Narragansett Bay. There was a preex- 

 isting valley, which was deeply and rapidly filled by detrital materials. It 

 is likely that this accumulation took place during a period of subsidence; 

 it evidently occurred after the deposits of the eastern trough had been 

 formed, and under conditions which led to the extravasation of large 

 amounts of lava. When the Connecticut Baain was subjected to compres- 

 sive action, the yielding was by the rupture and shearing of blocks, with 

 little trace of folding. It seems most probable that the hypothesis adduced 

 by Prof. W. M. Davis — which is, in effect, that the easily fractured planes 

 of the basement rocks of the area, which are composed of schists standing 

 at a high angle, induced the formation of faults x-ather than folds — accounts 

 for the departure of this region from the type of mountain building else- 



