THE CHESTER AMPHIBOLITE AND SERPENTINES. 103 



black center. Tlie weathered layer is distinctly softer, and although the 

 change to serpentine is not more advanced than in the interior, the olivine 

 fragments polarize much less brilliantly than in the black portion. They 

 may be referred to villarsite. 



In both the interior and the weathered crust occur (listautly scattered 

 spherules, about 10""" across, of a finely radiated tremolite-asbestos. Tliey 

 are not bounded by a true spherical sui-face outwardly, but long, delicate 

 needles, just visible with a strong lens, project far lieyond the average svir- 

 face. The impression is very strong that these latter are, as it were, feelers 

 thrust forward into the mass from a center of alteration. 



Many of the spheres are changed wholly or partly into talc, the change 

 starting at the center and following up the other to the periphery, and, 

 especially in the outer layer, resulting in the entire change of the spherule 

 into talc; and as the steatite bed into which the serpentine grades has the 

 same radiated fibrous texture, it has apparently been derived from the 

 latter after tlie same manner. 



These radiated tufts bear also some resemblance to the radiated asbestos 

 zone surrounding the garnets of the Saxon "garnet-serpentines," described 

 by Dathe,' though here no garnet center can be observed, and the radiating 

 mineral is much coarser than would accord with the description of the 

 Saxon occurrence. Indeed, garnet, so abundant in the next higher forma- 

 tion, is here curiously absent from the amphibolites and associated rocks 

 clear across the State. 



Slides of the freshest black portion of the rock appear under the lens 

 to be made up of angular grains of olivine, often quite complete crystals, 

 without admixture of anything else except a black ore arranged in rudely 

 parallel, interrupted lines. The bleached outer layer shows nothing ditter- 

 ent, except that the black ore is removed and tlie whole soaked full of 

 iron rust. 



Under the microscope the slides show the finest olivine network; the 

 broad meshes of chrysotile are beautifully develo})ed and occupy about a 

 thii-d of the area. The olivine is without inclusions, except small chronnte 

 octahedra, and rarely long series of straight, black needles, which are 

 arranged parallel to the vertical axis and at right angles to the length of 

 the series with the regularity of a micrometer, except that some lines are 



'Olivinfels, Serpentm, and Eklogit (lea sachischen Granulitgebietes : Neues Jahrbuch, 1876, p. 225. 



