THE CHESTER AMPHIBOLITE AND SERPENTINES. 109 



coarse, rajj^g'ed rock, made U)i of crystals of enstatite, often 10 x (i x 4"™ in 

 size; and no other original constitnent can be detected except dolomite, 

 which is inclosed in large, rounded grains in the freshest enstatite. Indeed, 

 in much of the mass the whole is made up of the large, imperfect, interlaced 

 prisms. These are thickly coated by a greenish-gray talc-like product of 

 decomposition, which also penetrates in thick layers along the i)erfect cleav- 

 age until the whole is changed into bastite aud ultimately into talc. Where 

 the change is more advanced, great sheets and remnants of the bastite, 

 gray-green in color, lie in a mass of black serpentine, or in a mixture of 

 this and a yellow dcdomite. Often, however, the enstatite rock seems to 

 degenerate into a talc-like mass without an}' trace of serpentine, and the 

 masses of black serpentine and dolomite may have originally contained 

 some other mineral besides the enstatite, though I could obtain no ])roof 

 of this. 



Under the microscope the enstatite, cut parallel to the perfect cleavage, 

 sho^^•s in the freshest portions only a few black microlites, but it is much cut 

 up by a network of yellow serpentine; and here large octahedra of magne- 

 tite appear. With convergent light it polarizes in bright colors, and, of 

 course, shows no axes, and on moving the slide spaces are found which 

 show the axes as in diaclasite, accompanied with bright colors, and these 

 parts are not distinguishable in ordinar}' light from the unchanged ensta- 

 tite. Moving the slide a little farther, one sees the axes as in bastite and in 

 paler colors, and in common light these parts have the appearance of ser- 

 pentine. The divergence of the optical axes is very small for the bastite, 

 certainly less than 30°. Embedded also in the black serpentine are, rarely, 

 large scales of a deep-green clinochlore, with divergence of the optical 

 angles of about 10°. 



By the roadside near the cemetery, southwest of the last locality, are 

 found bowlders of all the varieties of rock mentioned from this outcrop, and 

 several others of interest which seem also to come from this place, although 

 this can not be made certain. One great mass of limestone is in places 

 banded in dull black, from the large amount of magnetite in the limestone. 

 It shows also, under the microscope, a large number of fine actinolite needles 

 and rarely a grain of coccolite, and this piece is so exactly, in other parts, 

 like the tremolitic limestone found in place nortli of the serpentine knob 

 that it is scarcely possilile that one can err in assigning to them the same 



