344 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



In other slides, from near H. Winter's, the rock is greatly decomposed, 

 the feldspars are mostly kaolinized, the hornblende is broken up into a 

 network of actinolite and biotite, and only disconnected patches of the 

 black opacite remain. Secondary quartz and calcite appear. One feld- 

 spar was shown, by the position of the optical axes, to be orthoclase. 

 Here, and in sections from the south border, the plagioclase shows fine 

 undulatory extinction. In the coarse white variety from A. Pierce's the 

 feldspar is full of muscovite and the dark silicate is changed to an actino- 

 lite, with very strong transverse fissures. One feldspar, cut parallel to 

 M (cc F do), showed extinction — 35°-36-, with edge P M, indicating 

 anorthite. 



In fissures in the diorite beside the road near the old cemetery a large 

 quantity of pure-white radiated prehnite occiu-red. It was ^^roved, optic- 

 ally and by measurements under the microscope as well as by blowpipe 

 tests, to belong to this species.^ 



Leverett Center. — North and south of the road east from this place to 

 the point where this road turns south are outcrops of a massive rock which, 

 although greatly decomposed, gives every indication of having been a 

 diorite of the same type as that last described. With the lens the rock 

 is seen to be composed of saussuritic feldspar and coarsely cleavable 

 black hornblende, arranged with the texture of a gabbro. The feldspar is 

 often Included in separate grains in the hornblende, or rarely in pyroxene. 

 Its feldspars are generally wholly kaolinized, but their shape and arrange- 

 ment are exactly those of the Prescott rock. They show extinction of 12° 

 to 25°. The intervening hornblende Is mostly changed into a matted 

 mass of actinolite needles of weak pleochroism, or changed to serpentine, 

 but does at times polarize together over a considerable area, and shows 

 large patches of the black opacite, exactly as does the altered portion of 

 the Prescott diorite. Masses of menaccanite surrounded by leucoxene 

 are especially abundant, and the apatites are unusually large, 0.12°"" across 

 by 0.37°"° long. The rock presents both the varieties described under 

 the Prescott rock. Owing to the drift covering, its extent and relations 

 can not be well made out. 



' See under "Prehmte," in A mineralogical lexicon: Bull. U. S. Geol. Survey No. 126, 1895. 



