8 PROCEEDINGS OF THE ACADEMY OP [Jan., 



granite. Where three-eighths to one-half inch thick, chips of the rock 

 are procurable which permit of sections being made showing the 

 granite penetrated by the small dike. Here the matrix is an almost 

 opaque glass with plagioclase rods and phenocrysts of augite. When 

 it becomes three-fourths inch thick, a slight tendency toward crystal- 

 lization of the matrix is noticeable in the centre, "and so on until the 

 middle of the main dike is reached, where but little trace of the 

 basaltic texture remains and the rock is a characteristic diabase. 

 A similar series of sections can of course be made by starting from 

 the contact in one of the larger dikes, but the transition from basalt 

 to diabase is much more sudden. 



Two other rocks occurring nearby, but not appearing on the shore 

 line just considered, are worthy of mention. One is a highly por- 

 phyritic andesite with phenocrysts sometimes two inches long, 

 indicated by their extinction angles to be oligoclase, in a matrix 

 consisting of uralite, biotite, and plagioclase. This rock is not well 

 exposed at Pigeon Cove. I have noted an outcrop in a door yard 

 near centre of village and another in a hollow west of what is known 

 as Sunset Rock, but across Sandy Bay it appears as a sharply defined 

 dike in the granite, on the shore between Rockport and Straits- 

 mouth. As the granite here seems capable of cleaving in a straight 

 line for an indefinite distance and the three exposures are approxi- 

 mately in line, although widely separated, they may all pertain to 

 the same dike. The other rock referred to occurs in a cut leading 

 from the shore to the Rockport Quarry, near the archway under 

 main road. It is a light brown crystalline rock which proved to 

 consist entirely of micro-pegmatite, the best example I have seen of 

 this intergrowth of quartz and microcline. 



