60 GEOLOGY OF OLD HAMPSHIRE C0U2^TY, MASS. 



The quartz is often inclosed in the orthoclase in wholly rounded grains. 

 It contains great swarms of cavities of large dimensions and the most dis- 

 torted shapes, often spun out into long capillary tubes, which sometimes 

 connect distant ca\nties. Often these appear empty ; often they contain a 

 fluid with large, motionless bubble; sometimes they appear to contain two 

 fluids, Avith moving bubble; sometimes, also, they are negative crystals, 

 with very large bubbles. Entile needles occur rarely in the quartz. The 

 orthoclase is in large crystals intergrown Avith albite. The plagioclase 

 extinguishes at 25° to 28°, is optically negative, and is a lime-soda- 

 feldspar near anorthite. Large grains are free from multiple twinning, 

 except near the borders, where it is caused by pressure. 



The change of feldspar to muscovite is of great beauty. Often everj^ 

 other lamina of a triclinic feldspar is changed to a mass of fine nacreous 

 scales, the intervening laminae being unchanged. 



The biotite is red-brown, rarely green, and then associated with hex- 

 agonal scales of hematite. Zircon occurs in small, highly refringent prisms. 

 Garnet is in hyacinth-red grains and dodecahedra, inclosing smaller dodec- 

 ahedral crystals or cavities. There is no magnetite, menaccanite, or titanite. 

 Resume. — Friable, light-gray, medium to fine grained biotite-gneisses, 

 which, beyond the boundaries of the county, show abundant evidence of 

 their derivation from conglomerates, of which traces are not wanting 

 within the boundaries of the three counties along the western border, but 

 fail almost entirely in the three eastern areas. They are contrasted with 

 the older gneiss by the failure of all the peculiarities enumerated at the 

 close of the last chapter (p. 30) and marked by the abundance of titanite 

 in pale, flat crystals, both macroscopically and microscopically present. 

 This mineral is very rare in the older gneisses, except in or near limestone, 

 and it occurs there in larger and more sharply defined crystals. 



Beds of honiblende-schist are almost always absent. Important beds 

 of a fine actinolite-quartzite and of olivine-clu-omite-enstatite rock, with fine 

 contact phenomena, characterize the Pelham area. 



THE MONSON QUARRY. 



The following account, copied from the Springfield Republican of 

 May 9, 1884, and verified as to its accuracy, may find a place here, giA'ing, 



