McMAHON : PETROLOGICAL NOTES ON SOME PERtDOTlTES, ETC.; 



Olivine constituted the major part of the original rock. The 

 proportion of fresh olivine to serpentine in the hand-specimen 

 examined varies very much. In places olivine preponderates and 

 the field of the microscope consists of fresh olivine traversed by a 

 network of narrow canals filled with serpentine. In other places the 

 field consists of serpentine with small remnants of unaltered olivine 

 left in it here and there. 



The enstatite is colourless and polarizes feebly. It is cut up by 

 canals of serpentine and has evidently sustained considerable strain 

 and pressure. The lamellae are sometimes bent and strain shadows 

 are not uncommon. Some of the slices exhibit a lamellar inter- 

 growth of monoclinic pyroxene and enstatite similar to that described 

 by Rosenbusch. 1 They can only be distinguished from each other 

 in polarized light. 



The slices also contain some allo-triomorphic crystals of pyroxene 

 and some picotite. The structure of the rock is holo-crystalline. 



No. g4—2i7. Peridotite {Lherzolite) from Markha valley, Ladakh ; collec- 

 ted by R. Lydekker, F.RS. ; Sp. G. 2*976. 



This rock is composed of olivine, enstatite, augite and picotite. 

 Olivine is by far the most abundant mineral and enstatite comes next* 



The olivine is traversed by a perfect net-work of serpentine 

 canals, but is otherwise quite fresh. The enstatite has also suffered to 

 some extent in this way, but not so much as the olivine. Both 

 the enstatite and the augite are nearly colourless in transmitted light. 



The structure of the rock is holo-crystalline. 



Serpentines. 



No. 4 — 210. Serpentine, species Bowenite, from the Skiu valley, Shigar ; col- 

 lected by R. Lydekker, F.R.S. 



Mr. Lydekker in his Memoir on the Geology of Kashmir (Memoirs, 

 Geol. Surv. Ind., Vol. XXII), at page 189 refers to this serpentine 

 as follows: — (i In these shaly rocks (of carboniferous age) somewhere 



» Microscopical Physiography of the rock-making minerals, by Rosenbusch. Trans- 

 lated by Iddings; p. 205. 



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