292 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



the biotite against wliicli they rest. The hirge ainouut of coaly matter in 

 the centers of the biotites indicates that the rock was more carbonaceous 

 when the biotite was formed than at present. The biotite incloses garnet, 

 which was thus first formed, and the muscovite has also folded round the 

 garnets, forming small cups from which they fall, and has also, as above, 

 arranged itself symmetrically to the biotite, and is thus shown to have been 

 third in order of appearance. Leucoxene appears in yellowish-white grains 

 more rarely than in the argillite. 



Staurolite appears in some abundance in stout, shapeless masses nearly 

 large enough to be seen with a lens — red-brown by reflected light, nearly 

 opaque by transmitted light. They polarize distinctly, showing in the 

 thinnest places a mosaic of bright red and blue, indicating twinning, and 

 also traces of the square and prismatic sections of single crystals. Some 

 crystals giAang the proper angles of staurolite are white by reflected light, 

 from decomposition, and this I have seen macroscopically in the schists 

 around Vernon. Here the staurolite was removed in evei-y degree from 

 the network of quartz, until only a few brown grains remained, and at last 

 only a cellular network of white (juartz. 



15. Mica-schist from above, and east of the quartzite, Williams farm. 

 A dark-gray, fissile muscovite-schist, with pimpled surface of somewhat 

 coarser grain than the preceding. 



The ground is exactly the same colorless, scaly, coal-dusted mass as in 

 the lower schist, and presents with polarized light exactly the same appear- 

 ance upon a slightly larger scale. It differs by the development of the 

 transversely placed biotite into quite large crystals, visible to the eye Avheu 

 the rock is broken across the bedding, and these crystals foi*m most of the 

 pustules which rise on the cleavage surface of the plates. They are bounded 

 on the basal planes, as in the lower schist, by a line of larger muscovite 

 plates, but this is not at all so constant as in the former case. Scales of 

 muscovite are often intercalated in the biotite with magnetite and pyrite. 

 The mineral is a true biotite (meroxene), with p <C v and small divergence of 

 the optical axis. Limpid dodecadi-al garnets, magnetite, and p}Tite also occur. 



Microscopic staurolites, single crystals with oo P, go P ob, and P 

 measuring oo P /\ co P = 115°, co P y\ oo P c» = 112°, are quite common. 

 They are very impure and nearly opaque, sometimes crashed and the parts 

 separated. They are nearly white by reflected light. Some slides show 



