332 GEOLOGY OF THE NAEEAGANSETT BASIN. 



and always very dark or black rock, the color being due to its carbon- 

 aceous character. It is difficult *o determine whether to call this rock a 

 fine-grained sandstone or a gritty shale, since it is sometimes massive and 

 without cleavage and sometimes shaly. 



Fifth. This merges into shale, the structure being due to cleavage. 

 The micaceous elements of the sandstones here become very abundant- 

 Sericite is a common constituent; the color at a distance often appears rather 

 dark, almost black, especially where moistened by water; but at closer range 

 it usually shows a dark-blue color, the dark tint being evidently due to xhe 

 presence of ferruginous and carbonaceous matter. 



Sixth. Occasionally the dark-blue shale becomes black, contains much 

 carbonaceous matter, and is comparable with the coaly shales of the less 

 metamorphosed part of the basin. 



The types of rocks described above alternate in an irregular manner, 

 making it impossible at the present to treat of them otherwise than as a 

 geological unit. From Hazzard's quarry, a mile north of Saunderstown, to 

 the angle of the shore a third of a mile south of "Watsons Pier, the expo- 

 sures are almost continuous. Here it is seen that the shales are an important 

 part of the Carboniferous section on the western side of the bay, forming 

 from a third to a half of the total thickness of the rocks exposed. The fine- 

 grained sandstones are another important element. The coarse sandstones, 

 although a conspicuous feature farther inland, can here hardly form a fourth 

 of the total section. 



Away from the coast, westward and northward, the exposures consist 

 chiefly of sandstone, often coarse and conglomeratic. Finer sandstones also 

 occur, but shales are rather infrequent, excepting in the regions (1) imme- 

 diately south of Wickfordj (2) a mile south of Sandy Point, on Potowomut 

 Neck, and (3) a mile and a half directly south of the second locality. 

 This diminution in the relative amount of shale exposed toward the west 

 ia striking, and would appear to indicate a corresponding lithological 

 distinction between the shore exposures and the more inland part of the 

 Carboniferous series toward the west and north were it not for the prob- 

 ability that the more isolated hiland exposures represent chiefly the 

 harder, less eroded, and therefore at present more elevated beds of the 

 Carboniferous series, while the softer and less enduring rocks, including 

 the finer sandstones and especially the shales, exist in considerable thickness 



