462 Hawkins — Notes on the Geology of Rhode Island. 



ern boundary passing through a point south of the 

 junction of the Putnam Pike with the Rhode Island-Con- 

 necticut line, thence southward as far as Moosup Valley, 

 and from thence northeastward, its southern border pass- 

 ing, apparently, south of North Scituate (see map). 

 The Milford granite gneiss in the Blacks tone Valley- 

 Woonsocket region is similarly affected, where it has 

 intruded and embayed the margins of the green schists, 

 and torn off portions of them. On the east side of Nar- 

 ragansett Bay the granite gneisses show the same char- 

 acteristics. 



The green schists exposed in the region immediately 

 west and north of Providence are normally fine-grained, 

 greatly sheared rocks of essentially gabbroid compo- 

 sition (see analyses of green schists, Table II). The 

 schists "become coarsely crystalline ' ' near contact with 

 the granite at Neutaconkanut Hill, as observed by Emer- 

 son and Perry (op. cit., 29). Moreover, this coarseness of 

 crystallization increases in such measure as to cause the 

 appearance of the "diorite" of the above authors (idem, 

 44), which, as a type, on account of its origin, will be 

 referred to as the "pseudo-diorite," a name suggested by 

 Professor C. W. Brown, who also first conceived of its 

 formation in this way. "Little or no trace of crushing" 

 (idem, 44) is far more generally shown in the pseudo- 

 dioritic contact zone than in the adjacent schists. The 

 resulting rock closely simulates the true diorite in its 

 coarse groundmass of short black amphiboles in feldspar 

 (idem, 29). Some replacement of secondary pheno- 

 crysts has occurred (idem, 30) ; these phenocrysts are 

 either hornblende, as described (idem, 44), or pyroxene, 

 as observed in local drift material from Berkeley ; these 

 latter pyroxenes are nearly equidimensional, measuring 

 1 to 2 cm. or more in diameter, and showing bright cleav- 

 age at 87°. An analysis of this latter rock, which unfor- 

 tunately is not very fresh, is given in Table II (analysis 

 15). The pseudo-diorite zone is very irregular; in 

 places where the granite appears to be in contact with 

 the schist it does not even seem to be present sometimes ; 

 at other times it may be two or three hundred feet wide. 

 With it are associated narrow epidotic stringers that 

 extend beyond the pseudo-diorite zone often for some dis- 

 tance, it may be for tens or hundreds of feet, into the 

 adjacent schist. 



