JL. V. Pirsson — Geology of Conanicut Island. 373 



draw safe conclusions : in regard to the large phenocrysts, 

 since they contain apatite, titanite, etc., it may be said that 

 they are not the first products of crystallization while their 

 more or less idiomorphie outlines indicate that they are older 

 than the groundmass in which they lie. It is a striking fact 

 that the rock never contains any phenocrysts of quartz and in 

 this is unlike most peripheral facies, dike forms, etc., of granite 

 porphyry. And it is probably true that while granites with 

 large feldspar phenocrysts are not uncommon they rarely or 

 never contain corresponding phenocrysts of quartz as might be 

 expected from analogy with effusive forms — an indication that 

 they have been formed under different conditions. The 

 analysis of this granite yielded the results here presented. 



Si0 o 71*23 



TiO; -21 



A1 3 13-64 



Fe~ 3 t-70 



FeO 1-00 



MnO ._ -05 



McrO 0-V5 



CaO 2-31 



Na 3*55 



K 2 3-79 



H.;0 1-72 



Total 99-95 



Sp. G 2-690 



It is that of a typical granite in all respects and needs no special 

 comment. The water is of course from alteration. It may 

 be remarked here that in this as in the following analyses the 

 water was actually weighed as such during the process of the 

 analytical investigation. This analysis was made from a speci- 

 men taken from an outcrop on a little hill in the N.W. corner 

 of D 4, the freshest and best exposure found. From here as 

 one goes southwest and south the granite becomes more and 

 more dynamo-metamorphosed, and one of the most striking 

 examples and best exposures of this is found in a recently 

 worked outcrop just inside of Mr. J. Wharton's gate in the 

 middle of C 3. Here the rock has been much fractured, it is 

 full of slickensides and other evidences of shearing and pres- 

 sure. Under the microscope all the components are seen to 

 be broken and crushed ; they lie in a mass of broken material 

 which cemented together by secondary silica renders the rock 

 extremely similar to a metamorphosed grit It is indeed sim- 

 ilar to a grit only mechanically made. Epidote and other 

 secondary minerals abound. In other places as along the shore 

 of Mackerel Cove the rock exposures have suffered so much 



