Hawkins — Notes on the Geology of Rhode Island. -±55 



largely of lath-shaped labradorites of medium composi- 

 tion, near Ab ? An 5 , augite, biotite, and ilmenite. The 

 Rosiwal test yields percentages as follows : 



Ab 1 An 1 =47-75% 



Ab An 3 



= 7-51 



Pyi 



= 16-29 



01 



= 8-12 



11 



= 602 



Calcite 



= 13-92 





99-61 



The unusually high percentage of Ti0 2 indicated by the 

 analysis is notable, and the large amount of C0 2 in cal- 

 cite, which shows that the rock is not fresh. 



(3). The Gabbros. 



There are also several stocks of predominantly gab- 

 broid nature, included in the granite gneisses. 25 These 

 gabbro masses are often lenticular in shape and widely 

 separated in position. Such basic rocks are shown in 

 scattered areas throughout the northern part of Rhode 

 Island, and to some extent in its southern, western, and 

 even in its eastern parts. The most important ones are 

 at Cumberland Hill, Woonsocket, Ironstone Reservoir, 

 Pascoag, Chepachet, West Greenville, Smith and Sayles 

 Reservoir, Sneech Pond, Moosup Valley, and at Pres- 

 ton 26 and Wequetequock, 27 Connecticut. They are dis- 

 tinctly pre-Carboniferous, as indicated at the gabbro 

 outcrop at Huntington Avenue and Gaskill Street, Woon- 

 socket, which lies in the Carboniferous basin. Their pre- 

 cise age is unknown, although they are doubtless very 

 old, being older than any of the granite gneisses in the 

 batholith which underlies this region. They now appear 

 only in scattered fragments and groups of fragments, 

 roof pendants 28 which have partly sunk in the granite 



25 For various reasons, as hereafter enumerated, these gabbros are 

 regarded by the writer as original intrusive rocks and not as reaction 

 rims of granites. Epidote is formed by reaction of the granite upon 

 intrusion against the basic rock, as described below (see discussion of 

 the contact metamorphism) . (Compare Emerson, idem, 167-170.) 



^Loughlin, G. F., U. S. Geol. Surv., Bull. 492, 1912. 



27 Hatch, L. (unpublished thesis) . 



28 Daly, op. cit., 100. 



