234 GEOLOGY OP THE IsTABRAGA^^TSETT BASTK 



is at several points very distinct^ and a careful examination of the same seems 

 to indicate that the shales strike more nearly north-south, and dip at a low 

 angle eastward The stream indicates a line of fault between the shales 

 and the arkose beds. 



The relative age of the arkose beds and of the green Conanicut shales 

 is not known. The arkose beds are undoubtedly Carboniferous. They 

 give evidence of interbedded layers of somewhat carbonaceous shales. 

 Some of these shale layers were thin, and suffered enough erosion from the 

 variable currents present during the deposition of the grit to cause the 

 remnants of the shale layers to appear like fragments of shale inclosed in 

 certain courses of the grit. The green Conanicut shales are also Carbonif- 

 erous. But there is no gradation of the grit into the Conanicut shale 

 immediately to the north. Those parts of the arkose and of the Conanicut 

 shales actually exposed along Mackerel Cove are therefore not strictly of 

 the same age, although both are of Carboniferous age. A line of fault 

 separates them. Since neither the upthrow nor the downthrow of the fault 

 is known, it is impossible to determine by comparison of their exposure 

 which is the older. 



North of the eastern half of the gi-anite area is found a greenish rock, 

 here called the Dumpling rock. In places, especially in the northern out- 

 crops along the shore, it is purplish, looks very much like an argillite, and 

 seems to show genuine stratification. Farther south along the shore, at a 

 promontory, it seems to contain pebbles. Still farther south, however, and 

 along all the inland exposures, from the eastern side of Conanicut, along 

 the northern margin of the granite area, toward the cove, the Dumpling 

 rock is greenish in color, fine grained, of homogeneous texture, gives no 

 evidence of clastic origin, is cracked in all directions, and does not have 

 the appearance of a stratified rock. It bears a strong resemblance to the 

 greenish rock found along the southern Newport Cliffs south of Sheep 

 Point. To a less degree it resembles the greenish and purplish rock form- 

 ing the middle third of Newport Neck. The most northern outcrop of 

 this greenish rock is along the shore half a mile south of Jamestown 

 Ferry. Thence it extends inland for half a mile in a southwest direction. 

 Here the northern boundary seems to meet the southern in a sharp angle 

 (see map, PL XXXI). The granite area lies but a short distance southward, 

 and the northern border of the granite passes irregularly eastward, south of 

 the Dumpling rock area, at first about N. 70° E , then S 70° E. to the 



