Hawkins — Notes on the Geology of Rhode Island. 449 



Basic Igneous Rocks. 



Of basic igneous rocks there are three distinct types in 

 the region herein studied, viz: Green Schist, Diabase, 

 and Gabbro. 



(1). The Green Schist. 



. This occurs at several localities within the area under 

 consideration, namely, in the Blackstone Valley, north- 

 west of Providence, and in Johnston and Cranston, west 

 of Providence, where it is associated with white quartz- 

 ite, as already mentioned; in similar relations at 

 Premisy Hill, a small eminence 3 miles west-southwest 

 of Woonsocket; and in several scattered exposures 

 between West Greenville and Primrose. In the Black- 

 stone Valley it has been mapped by Emerson and 

 Perry (op. cit.) and assigned to the Cambrian (Marl- 

 boro formation). Other writers of earlier (Shaler, et 

 al., op. cit.) and later date (Warren and Powers, op. cit.) 

 would place it in the pre-Cambrian. (Compare also 

 Emerson, op. cit.) On account of lack of evidence, 

 determinations of the age of the green schist-quartzite 

 series have been made from lithologic similarity of these 

 rocks to others not visibly connected with them but of 

 known age (the Cheshire and Westboro ("Grafton") 

 quartzite; compare views of Emerson and Perry (op. 

 cit.) with those of Warren and Powers (op. cit.)). 

 ("Algonkian?" of Emerson). There are several local- 

 ities in the southern part of the State where the occur- 

 rence of green schists or slaty rocks has repeatedly 

 attracted attention. They have been enumerated by 

 Poerste (op. cit.) as follows: 



At Church's Cove, west of Tiverton Four Corners, and 

 southward to Little Compton, a series of greenish shales 

 is exposed, associated with rusty limestones intersected 

 by numerous quartz veins. Green schists and slates on 

 Sachuest Point are described, also those on Conanicut 

 Island south of Jamestown, in the vicinity of the 

 Dumplings, and those at Newport. At least two of these 

 localities show the greenish rocks only in the most uncer- 

 tain relations with the known Carboniferous sediments 

 and the other adjacent rocks, so that little is known of 

 their age, except that they are probably for the most part 

 pre-Carboniferous. The altered dioritic "dikes" of 

 "Paradise," near Newport, and a hornblende and 



Am. Jour. Scl— Fourth Series, Vol. XLVI, No. 272.— August, 1918. 

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