THE CHESTER AMPHIBOLITE AND SEKPENTINES. 99 



With a lens the sUde shows patches of separated grains of a yellowish, 

 shining mineral, and between these patches run broad veins of the amor- 

 phous greenish serpentine and many magnetite grains. 



Under the microscope the broad veins break up into a mass of very 

 fine bluish-white blades, and the same lie among and separate the brightly 

 polarizing grains, not after the manner of the olivine network, but so that 

 the grains seem to l)e scattered and woven into the mass of needles as for- 

 eign bodies, a single needle often lying lengthwise in a crevice between 

 grains. They are exactly like the grains of epidote in the epidotic amphibo- 

 lites. Large tracts of these grains polarize together and show a single axis 

 with rings of color. The colors are also not so bright as olivine usually is, 

 and it is probable that the mineral is epidote. 



.5. Serpentine. — Chester. Fi'om the upper portion of the same bed, at 

 its south end on Chester-Middlefield road. Rock shows original bedding in 

 laminpe 20-2.")™'" thick, and fine inti'icate jointing, the latter structure Ijrouglit 

 out by weathering, while the rock still cleaves along the planes of the first 

 structure and shows on these planes a brownish-gi-ay, shining surface and 

 a texture that is suggestive of the mica membranes of the sericite-schists 

 above, rather than of the hornblende-schists, in the continuation of which 

 it lies. The rock breaks with a harsh, fine-splintery fracture, is of rather 

 light greenish-gray color, translucent and mottled with black when wet. 



With lens the section shows, beside the large masses of magnetite, wavy 

 lines of fine grains of magnetite §"" apart, which run out and are replaced 

 by others. These are seen, in sections transverse to the bedding, to be 

 determined bv the cleavage planes mentioned above, and represent the 

 original fine foliation of the rock. 



The mineral shows under the microscope broad bands of fiber set 

 transversely, and many large areas of disconnected epidote grains, all 

 polarizing together. 



4. Serpentine. — Chester. From the same bed at the north line of Ches- 

 ter, 3^ feet from upper surface of serpentine bed and contact of sericite- 

 schist. Slaty rock, dark-gray, dull yellowish-green and translucent when 

 wet, with reddish-gray sheen on cleavage surface, as if from mica. 



The slide shows no large grains of ore, onl}^ fine magnetite dust an-anged 

 in lines running in various directions, and no unchanged grains of any 

 primary crystalline mineral. 



