304 GEOLOGY OF THE NAERAGANSETT BASIN. 



MIANTONOMY HILL AND COASTERS HARBOR ISLAND CONGLOM- 

 ERATES. 



MIANTONOMY HILL. 



A little over a quarter of a mile south of the top of Miantonomy Hill 

 coarse conglomerate is exposed, south of a house along the edge of a field. 

 It is again exposed northwest of the house, trending northward. Northward 

 it forms the entire structure of Miantonomy Hill. Interbedded sandstone 

 along the entire northern margin of the hill shows the conglomerate to be 

 apparently horizontal from east to west, but in fact dipping southward at an 

 angle of about 15°. There is apparently a low eastward dip at the 

 northeast angle of the hill. 



The pebbles of this conglomerate are of the largest size, at times more 

 than 2 feet long, and they have not been elongated. They are evidently of 

 the Purgatory type. 



Northward, between Miantonomy and Beacon hills, there is exposed 

 considerable dark-blue sandstone, shaly in places, dipping low southward. 



BEACON HILL. 



On the summit of Beacon Hill more conglomerate is exposed. The 

 pebbles on the average are of much smaller size and usually do not exceed 

 8 inches in diameter. The series has evidently been slightly folded by 

 an east-west thrust, as may readily be detected by following the line 

 between the conglomerate and the overlying interbedded sandstone at the 

 north end of the hill summit. The pitch is again about 15° S., and the 

 westward dip on the northwest side of the hill suggests that the conglomer- 

 ate is here descending into the valley. The conglomerate of Beacon Hill 

 evidently underlies the much coarser conglomerate of Miantonomy Hill. 



FIELD EXPOSURES. 



In a field west of Miantonomy Hill and just east of the railroad is a 

 series of coarse conglomerate exposures, striking N. 8° W. and dipping 

 45° E. The most western exposure has smaller pebbles, the more eastern 

 ones larger pebbles, some of these attaining a length of 1^ to 2 feet. 

 Fossil oboli were found in one of the pebbles. Interbedded sandstones 

 disclose the dip. This dip indicates a synclinal structure between these 



