468 Hawkins — Notes on the Geology of Rhode Island. 



A summary of the behavior of the CaO in the contact 

 zone between the granite and the green schist at Neuta- 

 conkanut Hill appears to be as follows : — 



The amounts of CaO present in the various types 

 analyzed are : — 



In In In In In 



Green Schist. Pseudo-Diorite. Xenolith. Modified Gr. Unchanged Granite. 

 CaO = 8-99% 8-00% 1-37% 4-57% -47% 



Comparison of the above amounts of CaO with the 

 amount of CaO originally present in the schist indicates 

 its distribution as follows : — 



CaO originally present: 



1-37% 

 CaO left in xenoliths : 



(15-24%) r 3.52% 



CaO forming calcite: 



(100-%) 7-62% (39-15%) 



CaO lost thr. metamorphism 

 I (81-76%) 4-10% 



I CaO assimilated by granite 



t (45-61%) 



If the limestones be metamorphic in origin, a source 

 must be found for the C0 2 required in the formation of so 

 much carbonate. The C0 2 must then probably be 

 regarded as derived from emanations from the intrusive. 

 That such discharge of C0 2 does take place is recorded 

 by Van Hise. 35 The fact that under such conditions cal- 

 cium silicates were not formed must then be regarded as 

 the result of the inferior strength of silicic acid com- 

 pared with that of carbonic acid under conditions of not 

 very deep burial, where temperatures and pressures were 

 not high (op. cit., 173). 



Closely associated with the limestone there are often 

 interesting deposits of steatite, with associated hydratecl 

 and carbonated minerals. These soapstones are com- 

 monly gray in color with obscure fibrous structure, and 

 occasionally carry veins of green foliated talc of a supe- 

 rior degree of purity (as at Manton and at Manville). 

 On the borders of the steatite areas, which are at times 

 50 feet or more wide, there are gradations into green 

 schist, suggesting a derivation of the soapstone from the 

 schist, supposedly by a weathering process (Van Hise, 

 op. cit., 24), although the possible action of heated waters 



35 Van Hise, C. E., op. cit., 960-970. 



