Hawkins — Notes on the Geology of Rhode Island. 467 



of 25 feet and more from the contact, small schist xeno- 

 liths 2 by 4 or 5 cm. are not uncommon in the granite, 

 which is dark colored, porphyritic, and surrounded by 

 and intermixed with schist. 



The amount of CaO in the green schist of Neutaconka- 

 nut Hill is 8-99%. Of this the granite has been able 

 to assimilate 4-10%. The small fragmentary xenoliths 

 of schist remaining in the granite retain 1-37%. The 

 residue which goes to form calcite deposits is thus about 

 3-52% of CaO, or an amount equivalent to 3-52% of the 

 original schist. As CaC0 3 this would be 6-28%. 



If 2-84 feet of schist be assimilated, in any portion of 

 the contact zone 2-84 feet wide, 10 feet deep and one mile 

 long, containing 5,554 cubic yards, or, in other words, 

 along a mile of contact line where the contact is 10 feet 

 deep and the granite is affected as the analysis indicates 

 for at least 25 feet from the contact : — 



CaO liberated as calcite = 195-5 cu. yd. 



CaC0 3 produced as calcite = 34906 cu. yd. 



For similar contact 



100 ft. deep CaC0 3 produced as calcite = 3,490-6 cu. yd. 



10,000 ft. deep CaC0 3 produced as calcite = 349,060- cu. yd. 



Contact lines are in all probability fully as deep as the 

 last figure noted. A careful and conservative estimate 

 of the actual volume of the limestone present in field 

 exposures is as follows : — 



Harris Quarries, total volume z= 465,275 cu. yd. 

 Dexter Quarry, total volume == 333,333 cu. yd. 



The Harris deposit consists of three limestone lenses, 

 probably disconnected and perhaps overlapping; the 

 total length between north and south extremities of this 

 series is about 1000 feet. The Dexter limestone is a 

 single lens located 2 miles east of the Harris quarries. 

 Its length does not much exceed 500 feet. 



Comparison of the above figures, especially those from 

 the Harris quarries, with the theoretical results obtained 

 from the analysis, seem to indicate that, given a suffi- 

 ciently deep line of contact between granite and green 

 schist, such limestone deposits as those here found might 

 have originated from contact action alone. The writer, 

 however, for reasons stated below, does not believe that 

 they actually are the result of such a process. 



