IGNEOUS ROCKS 455 



perience goes, the quartz of the quarry granite is not characteristically 

 blue, nor is what we should call "blue quartz" always characteristic of 

 this granite in the present area. With a lens, and sometimes without, 

 minute epidote grains may be seen, usually associated with the biotite, 

 and also occasional reddish garnets. 



In thin-section the rock is seen to consist of distinct crystals of albite 

 or albite oligoclase, finely twinned after the albite, less commonly the 

 Carlsbad law, and always more or less filled with minute grains or rods 

 of epidotic material and scales of white mica; crystals of orthoclase or 

 "gitter" microcline, somewhat kaolinized, in which are irregular thin 

 lamellae of albite, are rather sparingly present; quartz, sometimes as 

 irregular grains, but much more generally in the form of granular 

 mosaics; strongly pleochroic, dark greenish brown to yellow biotite in 

 shreds and. flakes, to some extent scattered, but usually strung along 

 through the rock in streaks and elongated patches in which grains, 

 crystals, and granular aggregates of epidote, garnet, and occasionally 

 orthite crystals, the latter margined by epidote, are present. Some epi- 

 dote and garnet occur sporadically. The feldspar crystals possess little 

 of definite outline, although the albite sometimes indents the microcline 

 and shows, of the two, a tendency toward more automorphic outlines. 

 The, quartz is often strung out into elongate granular streaks between the 

 feldspars, and with the mica gives a strongly gneissoid appearance to the 

 rock. 



The characteristic thing about this granite, as of all the hiotite gran- 

 ites of this and neighboring areas, in contrast to the riebeckite granite.-, 

 is that there are present distinct crystsih of sodic plagioclase and ortho- 

 clase or "gitter" microcline, the latter containing a little perthitically 

 intergrown highly sodic feldspar; that there is epidote and sometimes 

 garnet and orthite present, and that the dark constituent is biotite. 



This granite in the area here described differs from the quarry granite 

 at Milford in being in part more sheared, frequently with the develop- 

 ment of blue quartz and also of films of muscovite along the planes of 

 shearing. In the central and eastern parts of the area the granite is per- 

 haps rather finer grained than the quarry granite and not so greatly 

 sheared as to the westward. 



The intensely sheared variety is well exposed in several Grand Trunk 

 Railway cuts northeast of Woonsocket between the first and second roads 

 south of the State liue. In some places the rock has become in appear- 

 ance a mica scliist. The feldspar has been granulated with the quartz, 

 but occasionally retains its pinkish color. 



East of the gabbro near Iron Mine Hill the rock has a granulitic 



