PKECARBONIFEROUS EOCKS OF CHAENWOOD FOREST. 



343 



wavy and indefinite in outline, bearing a general resemblance to a 

 •cryptocrystalline structure common in devitrified rhyolites. On 

 rotating the stage other microliths appear in the dark parts ; and it 

 is doubtful whether any glass really remains. Minute quartz grains, 

 so far as they can be recognized, are not numerous. Most of those 

 present are from J to | inch. In outline they vary, being some- 

 times rounded or subangular, sometimes showing crystalline angles ; 

 they are often traversed by cracks ; occasionally they include a little 

 of the ground-mass and specks of viridite, but usually are fairly 

 clear, though here and there are a good many enclosures, some being 

 opacite, but many almost colourless, like minute cavities (fig. 2). The 



Pig. 2. — Portion of hrohen Quartz Crystal, with Inclusions of Matrix 

 minute Cavities (?), S,-c. High SJiarpley. (Enlarged.) 



felspars are rather decomposed and stained with ferrite ; but ortho- 

 clase and a plagioclase, probably oligoclase, can be recognized. Both 

 include numerous microliths of epidote, viridite, and perhaps another 



Pig. 3. — Felspar Crystal with Inclusions resembling Brown, 

 Glass, (^'C, High Sharpley. (Enlarged.) 



xather similar mineral, together with a substance much resembling a 

 brown glass * ; these often lie in the planes of cleavage (fig. 3). These 

 felspars are frequently in perfect crystals, but sometimes appear 



* The general aspect of these felspars is remarkably like those in many 

 trachytes. 



