470 Hawkins — Notes on the Geology of Rhode Island. 



which have taken place in the schist as follows, during 

 alteration to soapstone : — 



Almost complete loss of A1 2 3 . 



Some loss of Iron. 



Relatively enormous gain in MgO. 



Large loss of CaO, and also of Na 2 and K 2 0. 



Oxides thus lost to the schist are segregated in talc veins 

 or elsewhere in the vicinity, as shown in the case of the 

 narrow, irregular veins replacing green schist along 

 joint planes in the Manton Avenue quarry, adjacent to 

 the steatite deposits, containing the following minerals, 

 in their order of crystallization : — 



Pink orthoclase; short chunky crystals 1 or 2 mm. in 

 diameter, shown by petrographic examination to be Carlsbad 

 twins. Sheaf-like rosettes and typical crystals in cavities. 



Epidote; fine granular crystalline mass, forming slender 

 acicular crystals in cavities. 



Calcite, filling all remaining openings. 



The presence of epidote and of orthoclase argues in favor 

 of deposition by hot waters probably emanating from an 

 intrusive granite. 



Another contact deposit is to be seen just west of South 

 Foster (Hopkins' Mills), where the new State road 

 passes the white school-house near the top of the hill. 

 Here there is rather poorly exposed at least 50 feet of a 

 marbled gneiss composed of biotitic gabbroid material 

 thoroughly intruded in lit-par-lit fashion by granite, 36 

 and 25 feet from this, a 25-foot outcrop of a fine-grained, 

 rather impure looking limestone marble (shown upon 

 treatment with hydrochloric acid to contain about one- 

 fourth of its volume of silicates, resembling tremolite and 

 scapolite). Between the basic gneiss and the marble 

 there lies a vein deposit which appears to have been 

 formed as a result of the invasion of siliceous emanations 

 from a granitic intrusion, reacting with the gabbro or 

 limestone, or both. Pneumatolytic action of this sort is 

 shown by the presence of apatite. The irregular vein 

 deposit shows minerals developed as follows : 



Wernerite ; light gray, well formed individuals, some as large 

 as 3 cm. in diameter and 5 to 10 cm. long, tapering at the ends, 

 without definite terminations; within, they are fine grained 



36 Compare Emerson (idem, PI. V, Fig. A, and PI. IX, Figs. A and B). 



