Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/492

From Wikisource
Jump to navigation Jump to search
This page has been validated.
Dr. Mac Culloch on Quartz Rock.

from the transparent quartz grains with which it is intimately united in the fresh rock.

  1. The same rock in point of external aspect, but evidently formed of highly compacted and rounded grains of many different colours. from the same place.
  2. Brown quartz rock, of which the fracture is so little granular that it almost approaches to common quartz; semitransparent. From the mountains of Mar, Angus, and elsewhere, alternating with, micaceous schistus.
  3. The same rock, in the same situations, of various shades of red.
  4. An almost equal granular mixture of pure transparent quartz, and snow-white felspar, the grains amorphous. From Arisaig and Balahulish, with micaceous schistus.
  5. The same, but with fragments of felspar, hearing obscure marks of crystallization. From the latter place.
  6. Waxy and perfectly compact quartz, having a porphyritic aspect from imbedded fragments of felspar; accompanying the same rocks.
  7. White granular quartz rock of a moderately fine grain, containing at the same time large angular pieces of quartz, of a diameter from half an inch to many inches. In the same series at Balahulish.
  8. White granular rock consisting of felspar and quartz traversed by veins of pure white granular quartz, resembling in colour and texture the finest sugar. From Jura, and elsewhere.
  9. Distinctly rounded grains of the purest transparent quartz and imbedded in a mass of very fine grained white quartz. From the Cape of Good Hope.
  10. An uniform mixture of grains of transparent white quartz and opaque reddish felspar, containing rounded pebbles and fragments