Rocks of Noyang. 49 



examination prove to be really portions of the metamor- 

 phosed paleozoic sediments of the district. 



It remains uncertain which is the younger formation, the 

 white quartz-porphyrite, or this felsophyrite, but I incline 

 to consider the latter to be the younger of the two. 



This rock is intensely hard and flinty in appearance, 

 usually black or greyish black in colour, and shows 

 exceedingly numerous included fragments of other rocks, 

 which give to it a porphyritic appearance. I examined two 

 samples which I collected as probably fairly representing the 

 average character of the rock. The microscopic examination 

 of the two samples gave me the following results : — 



The first sample consisted of a very large proportion of a 

 basis of various shades of yellow to brown, and which has 

 undergone felsitic alteration. It shows flow structure in a 

 beautiful manner, not only in the differently shaded bands 

 of varied width, but also in narrow lines of black, opaque 

 granules, or long and narrow black microliths (iron ores) 

 which lie in the direction of the flow. Alternating with 

 these bands of almost wholly basis are others which are 

 crypto-crystalline, and resemble the ground-mass of the fine- 

 grained porphyrites. In these crystalline bands there are, 

 however, strings and patches of basis which show very 

 distinctly when a Klein's quartz-plate is used for their 

 examination. Although the crystalline bands are much 

 smaller individually than those of basis, and ■ in the 

 aggregate do not probably make up more than one-fourth 

 or one-third of the mass, yet in places they swell out to 

 several times their usual breadth, and the individual crystalline 

 grains become at the same time larger. Similarly, the 

 bands of basis swell out and narrow in their course. The 

 manner in which these bands divide and follow round the 

 included fragments is very characteristic. 



Included in these bands, but more especially in those of 

 basis, are innumerable minute crystalline grains, some of 

 which are of felspars, which in many cases are twinned. 



In this ground-mass, if the term is admissible, are 

 included many much larger fragments — 



(a.) Angular masses of yellow glass, rendered in places 

 almost opaque by iron ores. 



(b.) Fractured and eroded crystals of quartz, such as are 

 found in the quartz-porphyrites. 



(c.) Felspars which are more or less fractured. Almost all 

 of these are twinned. The optical measurements which I 





