102 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



of any other locality in the range. It is dark-gray, scarcely shaded with 

 green, spotted full of primary magnetite in large gi-ains, and weathering 

 uuiforndy through light green to fawn color. It is very compact and tough 

 and much jointed. A qualitative analysis detects about 1 per cent of chro- 

 mium in the specimen from which slides were cut (Dr. A. J. Hopkins). 



With the lens the slide shows no trace of magnetite dust, but is frosted 

 all over with shining grains of a yellowish-white crystalline mineral. 



Under the microscope the ground is a confused tangle of bluish-white, 

 rhombic needles of extreme fineness, and the shining grains, polarizing 

 brightly, are scattered in it so much like foreign grains that I suspected the 

 slide to have been badly cleaned of the corundum used in polishing, and cut 

 new ones carefully, but with the same result. The mineral polarizes with 

 about the brightness of pyroxene; tlie angular grains are fresh to the edge 

 and show no cleavage; some of the larger show a single axis with rings of 

 color. It does not gelatinize with hydrochloric acid. For analysis, see 

 page 116. 



8. Olivine-serpeutinc. — Osborn's soapstone quarrj^, Blandford. Eastern 

 bed. (See fig. 5 and page 87.) 



Except one specimen from Chester, whose exact location is not known 

 to me (Massachusetts Survey Collection, XIII, No. 53, described on p. 101), 

 this is the only bed in the long series of outcrops west of the river which 

 contains olivine in abundance. In all the beds hitherto mentioned its occur- 

 rence could at best be rendered only probable, thougli I have little doubt 

 that it was formerly present in many cases. In all the beds discussed below 

 the absence or rarity of oli\'ine is equally certain, and the derivation of the 

 serpentine from pyroxenite or coarse enstatite rock is quite clear. Indeed, 

 much of tlie rock is so little changed that it could he as pro})erly called 

 enstatite rock as serpentine. 



The great mass of the rock where freshest is dull-black, opaque when 

 wet, with the marked shining, greasy luster characteristic of those serpentines 

 which still contain oliAane in abundance. It gelatinizes abundantly with 

 acid, and the solution contains magnesium and iron, with trace of calcium. 



A layer of surface decomposition of a drab or grayish olive-green color 

 and 10-20""" thick covers the surface, and is sharply demarcated from the 

 black interior. It is caused largely by the removal of the black ore, and the 

 rock within its limits has much more the look of ordinary olivine than in the 



