SEPARATION FROM THE SEA. 37 



Lesquereux's conclusions were obtained from beds which lie at 2,000 to 

 3,000 feet above the base of the Coal Measures as found in this basin, 

 and that the beds whence his fossils were obtained do not extend nearer 

 than 2,000 to 4,000 feet to the top of the highest remaining beds of 

 Carboniferous age which are found in this area. It is of course possible 

 that the lower portions of the section, the fossils of which have not yet. 

 been studied, may prove to belong to the lower Coal Measures, but the 

 essential lithological similarity of the beds below the upper conglomerates 

 makes this view improbable. So, too, the lack of paleontological evidence 

 concerning the precise age of the upper conglomerates permits the suppo- 

 sition that they may belong to the Permian period. 



ORIGINAL RELATION" OF THE NARRAGANSETT BASIN TO THE SEA. 



It is noteworthy that no trace of marine fossils has been found in any 

 portion of the Carboniferous section in this basin. Moreover, there are no 

 limestone pebbles which would lead to the suspicion that beds of this origin 

 had ever formed a part of the original sections. A few limy deposits which 

 occur in the northwest portion of the area appear to be the results of infiltra- 

 tion, and to be classable as A r eins. When we consider that the Carboniferous 

 section of the West Appalachians exhibits evidence of frequent intrusions of 

 the sea, the question arises how a basin having the stratigraphical profundity 

 of that of Narragansett Bay could have been developed adjacent to the 

 shore line without having, in its repeated subsidences, experienced marine 

 invasion. At the present time the bottom of this basin lies several thousand 

 feet below the plane of the ocean waters which penetrate it. Even before 

 the mountain-building movements which have deformed the rocks began, 

 it is probable that the basin had something like its present depth. 



The conditions of the basin, as above noted, lead to the conclusion that 

 during the Carboniferous period it was continuously separated from the sea, 

 and therefore had the character of a lake, or perhaps that of a broad river 

 valley. As it was evidently the seat of very considerable drainage, the out- 

 going water might have excluded, in a sufficiently effective way, the pene- 

 tration of the oceanic waters, even though the plane of deposition was not 

 much above the marine level. When, however, we consider how subject 

 all coast lines appear always to have been to oscillations of level, it seems 

 most reasonable to suppose that the basin lay always at a considerable 



