380 GEOLOGY OF THE NARRAGANSETT BASIN. 



CONANICUT AJRKOSE. 



On the eastern side of Mackerel Cove arkose is found exposed north 

 of the granite area. It is evidently composed of the detrital material 

 derived from the granite, and the latter is considered pre-Carboniferous. 



The statement that the arkose underlies the green shale is an assump- 

 tion. The thin arkose layers in the black shale at Beaver Head should be 

 noted in this connection, since they evidently occur at the base of the 

 Aquidneck shale series. Possibly the Mackerel Cove arkose is also con- 

 temporaneous with part of the Aquidneck shales. 



ROSE ISLAND AND COASTERS HARBOR ISLAND ARKOSE. 



Arkose and black shale occur on Rose Island and at the southern end 

 of Coasters Harbor Island. The writer has felt strongly inclined to consider 

 the arkose exposed on Conanicut and on the islands last mentioned as 

 deposits formed in the proximity of a great pre-Carboniferous granite area, 

 without any attempt to closely synchronize the various exposures. Thus, 

 the arkose at the southern end of Coasters Harbor Island may belong, as 

 far as relative age is concerned, higher in the Carboniferous series than 

 the arkose on Conanicut Island. The fact that it appears so close to the 

 coarse conglomerate on Coasters Harbor Island suggests this. But this is 

 another point which must be left doubtful. 



If the green and purple shales of the Newport Harbor Islands, of New- 

 port Neck, and of Sachuest Neck are of Cambrian age, as suggested, these 

 shales, together with the granite, probably formed exposed land areas in 

 the near vicinity in early Carboniferous times. The progressive overlap- 

 ping of Carboniferous deposits caused arkose beds to be formed, resting 

 upon the lowered Cambrian formations. This would account for the close 

 geographical association between arkose and green shale or other pre- 

 Carboniferous rocks in these areas. Faulting has obscured this relation. 1 



Arkose is also found west of Ochre Point, east of Newport. Perhaps 

 in all of the cases here cited, from Conanicut, Rose Island, Coasters Harbor 

 Island, and west of Ochre Point, the arkose is to be considered as contem- 

 poraneous with some part of the Aquidneck shale series. 



The arkose on Conanicut may reach a thickness of 100 feet. The 

 deposits on Rose Island and Coasters Harbor Island are much less thick. 



1 T N. Dale, Am. Jour. Sci., 3d series, Vol. XXVII, pp. 217-228, 282-289, map, 1884. 



