CAPE COD GEOLOGY 



225 



Point Judith Neck, east shore, 1| miles south of Narragansett 



p ier S. 19° W. and 



S. 29° W. 



Little Neck above the Narrows S. 27° W. 



These glacial striae at places examined in succession southward show an 

 increasing trend westward, which is a normal result of the outward curvature 

 of the lines of flowage of the bottom ice in a glacial lobe. The island bears between 

 15° and 37° west of south from Point Judith, and it came well within the reach 

 of ice moving down the west side of Narragansett Bay and deploying as a lobe 

 between Gay Head and the interlobate axis described above. 



UPPER CAMBRIAN QUARTZITE PEBBLES 

 Waterworn fragments of an Upper Cambrian quartzite or sandstone con- 

 taining small fossil branchiopods are found on the beaches of Block Island. Such 

 fragments are found also in the Carboniferous conglomerate near Newport, R. I., 

 as well as farther north, in the Rhode Island coal field. Walcott found some 

 among the pebbles on the beach at Westerly, R. I. 



AGATES 



Fragments of impure or clouded or banded red and white agate are found 

 on the beaches of the island, as well as in the oldest Pleistocene deposits at 

 Clay Plead. Some fragments as large as 6 inches in diameter have been seen 

 on the beach south of Clay Head. Some pieces of this agate contain a trace of 

 a reddish shaly country rock, which suggests that they were brought from 

 the area of red Carboniferous beds that are associated with volcanic rocks 

 and veins of quartz in the country between South Attleboro and North 

 Attleboro, Mass., and Diamond Hill, R. I. The mass of quartz at Diamond 

 Hill bears the closest resemblance to these agates, but so far as is now known 

 no agate has been found at Diamond Hill. The pebbles of agate are found on 

 the beaches on Block Island, on the north shore of Marthas Vineyard, and 

 as far east on the Elizabeth Islands as Tarpaulin Cove. The southward fanning 

 of these small erratics is like that of the Cumberland iron ore, but the fan extends 

 farther eastward. Cumberland Iron Mine Hill and Diamond Hill, in Rhode- 

 Island lie respectively 3 and 5 miles east of Woonsocket, and the eastward 

 fanning of the drift tailings is consistent with the positions of the Diamond 

 Hill quartz mass and Iron Mine Hill. 



Along with the agate pebbles on the beaches at Naushon, on Marthas 

 Vineyard, and on Block Island there are vein quartz pebbles having the peculiar 



