108 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



The perfect sahlite cleavage is also retained after the change to serpen- 

 tine is far advanced, and shines ont when the piece is held in a particnlar 

 position as single faces luster-mottled with small opaque spots of serpentine. 

 In the process of change, black iron ores in rods and lines of dots appear 

 in the interstices of the tremolite needles, as well as in the prismatic and 

 pinacoidal cleavage of the sahlite ; and after the serpentinous change (which 

 commences in the transverse cleavages of the tremolite and advances in a 

 network somewhat like that in oliAane) has completely transformed the 

 whole into a confusedly polarizing mass, the acute-angled netwt)rk is as 

 clearly marked in ordinary light as before l)y the black lines, and in places 

 traces of the rectangular pyroxenic cleavages can also be seen. 



In the most completely changed portions blades of actinolite, either 

 later formed than the tremolite or more resistant than it, show marked ple- 

 ochroism for so nearly colorless a mineral — pale blue-green to ocher-yellow. 



10. Enstatite-serpentine and steatite .—K-Avt\?a\A, Connecticut, just south 

 of the town line, where the road from West Granville to Hartland crosses 

 Hubbard Brook. On passing 100 feet up the slope southwest of the bridge 

 the black enstatite-serpentine occurs in force. It is of finer grain than the 

 other beds to the north, with which it otherwise agrees exactly, and it is 

 largely changed to steatite. 



11. Tremolite rock and enstatite-serpentine. — J. Downey, Granville. Fol- 

 lowing a wood road east into the densely wooded swamp from a point just 

 north of the house of Mr. J. Downey, I came upon a very interesting out- 

 crop, Avhich represents the first occurrence of sei-pentine upon the amphibolite 

 band, where, after turning nortli, it swings around the gneiss of Granville. 



Along east of a band of the conmion amphibolite there crops out a 

 low ridge of limestone, at times quite pure, light-gray, and thin-fissile, 

 but taking more and more very fine tremolite into its composition, until 

 it comes to be a flat-fissile, pale-green tremolite-schist, almost as fine- 

 grained as nephrite, which it somewhat resembles. It polarizes brilliantly, 

 has extinction in maximum 27°, and shows a few straight, black microlites 

 and a few large grains, also visible to the eye, of a black magnetic ore. It 

 gives on analysis only traces of AkOr,, FeO, and CaO, and is an almost pure 

 silicate of magnesia. 



South of this there are no exposures for a short distance, and in the 

 strike of the tremolite rock rises a great knob of enstatite rock. It is a 



