1893.] NEW YOllK ACADEMY OF SCIENCES. 211 



SO abuudaut as to make tliem true tourmaline grauites. AuutLer 

 phase, wliich has been distinguished as granulite* (perhaps 

 unfortunately, as it lacks the foliation of a typical granulite), 

 occurs at man}' points. It is fine grained and white, resembling 

 sandstone. Untler the microscoj^e it is seen to be a mosaic of 

 quartz and feldspar, with numerous larger individuals of garnet. 

 There is wide variation in the character of the feldspar, but 

 microcline is often conspicuous. 



The garnet usually shows crystal outlines, though irregular 

 grains are also present. It has a decided pink color and inclu- 

 sions are abundant. These have, as a rule, the shape of nega- 

 tive crystals, and are more or less concentrated toward the 

 centers of the crystals. With the exception of some apatite 

 and zircon, other minerals are lacking. The field relations of 

 the granulite and ordinary granite show a perfect continuity 

 between the two rocks, and suggest that the two varieties are 

 due to a differentiation of the original magma. But under the 

 microscoiDC the granulite shows a marked cataclastic structure, 

 together with a large amount of secondary quartz and feldspar. 

 It has clearly been formed from the ordinary granite by the 

 shattering of the constituents of the latter rock, attended by a 

 large amount of recr^stallization. 



In one portion of the granitic area there are several alterna- 

 tions between the ordinary granite and a very dark rock com- 

 posed of hornblende, biotite and plagioclase — a quartz-free 

 diorite in composition, though lacking the structure of atypical 

 diorite. The passage from the ordinary granite to this diuritic 

 variety is very gradual, there being no break whatsoever between 

 them, and there can be no doubt that the diorite is a basic 

 segregation from the original magma. 



The effects of dynamo-metamorphism upon the granite, while 

 almost always apparent, are not, as a rule, very conspicuous. The 

 bending, stretching and crushing of minerals have been men- 

 tioned, but these effects are generally to be seen only with the 

 aid of the microscope. Small areas of the rock, however, often 

 show incipient foliation, and at some outcrops the granite 

 passes into a true gneiss, which is, however, entirely distinct 

 from the older gneiss previously described. The formation of 

 granulite has already been mentioned. As to why the granite 

 sometimes changes to gneiss and sometimes to granulite, there 

 is no very clear evidence- But comparison of sections of the 

 two varieties indicates that the granulite results from a more 

 complete shattering of the granite, to which, with the absence 



* Trans. N. Y. Academy Sciences, XIL. p- 105. 



