Hawkins — Xotes on the Geology of Rhode Island. 165 



the nepheline syenites and related rocks in Ontario, Can- 

 ada, finds in general the same transfers taking place. 33 



It was probably on account of the abundance of avail- 

 able silica in the solutions accompanying the Rhode 

 Island granites that no rare rocks were formed. It will 

 be noticed, however, that of all the materials exchanged 

 in this process of contact metamorphism, the lime is 

 apparently the most easily displaced. Some of this lime 

 the granite has assimilated, as is shown by its abnormally 

 high content of CaO. A considerable portion of the lime, 

 however, which is not found in the original rocks on 

 either side of the contact, has been expelled, reappearing 

 as calcite veins, shown near the granite contact on the 

 east slope of Neutaconkanut Hill and in similar relations 

 on the west slope (compare Emerson and Perry, op. cit., 

 25). A reasonable enlargement or extension of this 

 action leads us to a consideration of Professor Brown's 

 further suggestion, that the limestone deposits of Lime- 

 rock and elsewhere in that part of Rhode Island might be 

 entirely the product of contact metamorphism resulting 

 from invasion of the green schist by granite batholiths 

 at considerable depth. 



The limestones of the State, belonging to what Emer- 

 son and Perry have called the Smithfield limestone mem- 

 ber of the Marlboro Formation (op. cit., 16 et seq.), are 

 crystalline marbles appearing as lens-shaped bodies, 

 usually in the green schist, often near its contact with 

 the granite, though at times wholly surrounded by the 

 granite itself. The total volume of limestone repre- 

 sented is probably somewhat more than a million cubic 

 yards. Much of it is a very pure limestone ; parts of it 

 are more or less magnesian, and the marginal portions, 

 for thicknesses at times as great as ten feet next to the 

 schist walls, are often dolomite. This latter fact might 

 be attributed to segregation in metamorphism, although 

 it may of course have been an original feature. Irregu- 

 lar zones are filled with pure white bladed and fibrous 

 tremolite (shown to be such in the thin section), which in 

 one sample of limestone from the Dexter quarry was 

 found to constitute 80-54% of the rock, the remaining 

 1946 % being all that was soluble in boiling- hydrochloric 

 acid. According to Van Hise 34 such silicification in 



33 Fore, W. G., this Journal, 40, 413-436, 1915. 



Si Van Hise, C. E., IT. S. Geol. Surv., Mon. 47, 971, 1904. 



Am. Jour. Sci. -Fourth Series, Vol. XL VI, No. 272.— August, 1918. 

 17 



