042 Granite at Mounts Adam and Eve. 



and microperthite. The mieroperthite may be a secondary result, 

 and due to the development of albite along cleavage planes from 

 incoming soda solutions. This view has been held both abroad and 

 here, where the microperthite has been found alike in districts of 

 regional metamorphism, and in gneisses regarded as altered sedi- 

 ments. The undulatory phenomena that accompany dynamic dis- 

 turbances are not lacking, though not especially notable in the slides. 

 Plagioclase is, as stated above, often in excess. 



The hornblende is a dense black variety that becomes transparent 

 only in the thinnest sections. It then appears yellowish-green, 

 parallel a; black, parallel b; deep green, parallel C- Brown biotite 

 is in much less amount. On Round Hill, however, to the north it 

 is the only dark silicate in specimens from the summit. Allanite is 

 frequent in the granite from the quarries on Adam and Eve, and 

 also in especially large amount in rather coarse pegmatitic masses 

 of feldspar and quartz, that occur in the granite, and that cause 

 imperfections in the stone. These contributed to the failure of the 

 enterprise on Mt. Adam. The allanite is at times in well-bounded 

 crystals, but of these the best were collected in the early days of 

 the openings and near the surface. The specimens are in all large 

 collections of minerals. At present, rude crystals and masses are 

 the only ones found. The mineral is so extremely brittle that the 

 crystals, when fairly well developed, were almost always shattered to 

 pieces when we tried to get them out. In sections, the mineral is 

 yellowish-brown to seal-brow^n, and as usual is strongly pleochroic. 

 It becomes dark and almost opaque on revolving the stage. The 

 mineral is so opaque, and withal so brittle, that it is not easy to 

 get a satisfactory section. It is almost always accompanied by 

 purple fluor spar, which appears along the edges of the crystals. 

 It is also, at times, bounded by a lighter colored brown rim of what 

 is probably slightly decomposed allanite. The optical properties of 

 the Edenville allanite have been measured by Michel-Levy and 

 Lacroix, who determine the mean index of refraction to be above 

 1.78, and the difference between the greatest and least indices to be 

 0.032. (Bull. Soc. Min. Trans., xi, 65, 1888.) 



The comparative abundance of this rare mineral is interesting. 

 The elements of the cerium group seem especially associated with 

 the granites along the belt of white limestone. At Franklin Fur- 

 nace allanite is very abundant, alike in the granite dike that pierces 



