LADAKH, NORTH-WESTERN HIMALAYA. 329 



not fresh and are dotted and streaked with on opaque substance, 

 dead white in reflected light, suggestive of leucoxene. 



I cannot say decisively from the microscopical examination of 

 thin slices of this rock whether it is a fine-grained grit made up mainly 

 of fragments of igneous rocks, or whether it is of true pyroclastic 

 origin. Three things, however, may be positively affirmed regard- 

 ing the rock, namely, that it is of clastic origin ; that the materials 

 of which it is composed are not water-worn, and that they cannot 

 have travelled far. Presumably, therefore, it is an ash. 



EXPLANATION OF PLATES XVII AND XVIII. 



Fig. 1 . Shigar bowenite as seen under the microscope between crossed N icols. 



Fig. 2. A fine-grained slice of Afghan bowenite under crossed Nicols. 



Fig. 3. Large grained Afghan bowenite seen between crossed Nicols. It is 

 composed of leaves of serpentine (antigorite). On revolving the 

 crossed Nicols, the dark portions become light and the light por- 

 tions dark. 



Fig. 4. Augite partially converted into fibrous serpentine (chrysotile). 



Fig. 5. Augite penetrated by large solution veins, filled with fibrous serpen* 

 tine (chrysotile), continuous with the chrysotile surrounding the 

 augite. 



Figs. 1— 5 are collotype reproductions of photographs taken by the author. 

 Some of the photographs have been enlarged in order to make the 

 micro-structure visible in the printed plates. 



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