•50 Rocks of JSToyang. 



was able to effect gave angles between 4° and 19° for the 



zone OP— ooP oo ; and in one crystal, which was perfect and 

 simple with the planes OP - P - o>P, I found the angle formed 



by the plane of vibration with the edge ooP oc- coP oo to 



be 5°. 



The felspars are extraneous to the rock, being merely 

 included fragments, and the optical measurements afford, 

 therefore, very little information except as to the individual 

 crystal in which the measurement was made. The second 

 sample showed, microscopically, a large number of inclusions, 

 and was not so black and flinty iu appearance as the other. 

 The colour was a greyish black, and I found the specific gravity 

 to be 2*717. Under the microscope I observed its charac- 

 teristics to resemble those of the former sample, but the 

 basis to be much less in amount, while the bands containing 

 opaque black bodies, the crystalline bands, and the foreign 

 inclusions were proportionately greater. This rock has the 

 following composition : — Bands of yellow basis, alternating 

 irregularly with bands or streams of micro-crystalline 

 materials. These bands are, as a rule, exceedingly narrow 

 relatively to each other, but in places swell out to bunches, 

 in which are usually contained angular fragments of foreign 

 substances, such as quartz or felspar. In this ground-mass 

 are — 



(a.) Angular fragments of quartz-crystals. 



(6.) Angular fragments of micro-crystalline-granular 

 quartz-porphyrite. 



(c.) Felspar crystals similar to those spoken of in describing 

 the last sample. The most peculiar feature in these felspars 

 is their conversion in some parts almost wholly into a pale 

 green mineral, having the optical characters of epidote. This 

 alteration, or more properly substitution, product also occurs 

 in several flows which traverse the slice. 



(d.) Two comparatively large "masses of fine-grained 

 sandstone are also included. These have precisely the 

 characters of the hornfels produced by the metamorphism 

 of the quartzose sediments of the district. 



(e.) Finally, traces here and there of some chlorite mineral. 



This rock may therefore be described as a felsophyrite, 

 having a ground-mass which, probably, if found free from 

 included fragments, would represent " pitch-stone." 



The composition of this rock, being made up so much of 

 extraneous materials, decided me not to take the trouble of 



