OP ARTS AND SCIENCES. 319 



of Mt. Mica, being a granite, with all its components (quartz, ortho- 

 clase, clevelandite, muscovite, black tourmaline, etc.), in very lar^e 

 masses. At the eastern end of the ridge there are several places 

 where a very pure quartz is quarried in immense quantities. The 

 peculiar mica is found at one of these quarries at points on the border 

 of the quartz deposit. The coarser and less well formed specimens 

 are imbedded in quartz and feldspar ; the finer and well formed are 

 usually enclosed in feldspar alone. One vertical face of the quarry 

 presented a most interesting exposure. Here the mica stood out in 

 bosses, or huge breasts, looking like broken spheres developed from 

 numerous centres, and grouped very irregularly. The spherical sur- 

 faces, on analysis, consisted of groups of rhombic figures, each repre- 

 senting a crystal of mica, with curved cleavage and tapering to the 

 centre of the sphere.'' 



Thus it appears as if these crystals were the result of two distinct 

 tendencies acting together, one concretionary, exerted to make the 

 mass solidify from centres, and the other the crystallizing force, tend- 

 ing to form at the same time the rhombic prism of 60° and 120° so 

 characteristic of the mineral. 



