52 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



scale by a decoraj^osition which has resulted iu the formation of a mass of 

 soft, greasy scales of venniculite (D' fig. 4), which, when boiled with sul- 

 phuric acid, yields a residue of white scales of pure silica. This has been 

 named pelhamite by Prof. J. P. Cooke, and thus the town of Pelhani has 

 lent its name to two equally poor ramerals. 



PETROGHAPHICAL DESCRIPTION. 



1. Saxonite, or oHvine-enstatite rock (pelhamine, Shejiard). This is a very 

 fresh mixture of olivine and enstatite, both dusted thi'ough with black ore, 

 largely chromite. It is a dull-black rock of very great toughness. The 

 olivine grains have often many crystalline faces. The eustatite is in rare, 

 small plates, with parallel sides and irregular ends, and with a fine wavy 

 lamination, which is often marked by lines of black ore generally concen- 

 trated in some part of the plate, especially the center. Although nearly 

 colorless or pale bi'ouzy in common light, it has marked jjleochroism. It is 

 plainly rhombic, and grades into the asbestiform decomposition product in 

 veins running through the section. The distant, strongly marked transverse 

 cleavage so common in enstatite is wanting. 



2. Secondary asbestiform antJiophyllite occurs iu the altered saxonite in 

 clear gray masses parallel or matted fibrous, in the former case so fine- 

 grained as to resemble silicified wood, in the latter made up of a mass of 

 short needles without radiated structure. It has very harsh feel. With a 

 lens it seems to be entirely fresh, transparent, and colorless, the gray color 

 being due to disseminated magnetite, which is -sasible, and may be removed 

 fi-om the jJOwder by a magnet. 



Under the microscope it presents a mass of colorless needles and blades 

 with delicate longitudinal striation, which breaks off here and there against 

 a transverse cleavage. The needles are broken across by a distant fracture 

 not exactly at right angles to the length.. Long, fine, straight needles, 

 breaking up at times into a row of grains, are present, and though not very 

 abundant, are concentrated more in the center; they appear black, bi;t at 

 times red with high powers. In crystals cut across the blades the form and 

 cleavage of hornblende can l)e detected, and I was able to separate and 

 measure one needle, obtaining 55.30°. They polarize brilliantly, and always 

 strictly as rhombic crystals, and this is the case with the silky asbestos. 



3. The plagioclase-feldspars of the contact zone. Professor Shepard 

 analyzed the two varieties of massive triclinic feldspar found in the great 



