Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/494

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Dr. Mac Culloch on Quartz Rock.

parallel mica, so thin as not to be discovered in the cross fracture. From Fassafern, Balahulish and Tyndrum.

  1. The same rock, but the layers of mica more conspicuous and undulating. From Balahulish.
  2. The same passing into mere mica slate. From the series at Balahulish and Tyndrum. These demonstrate the alternation of the quartz rock with mica slate.
  3. A large grained breccia consisting of fragments of quartz cemented by a mass of earthy white felspar, approaching to porcelain clay. From Jura.
  4. A rock consisting of felspar and granular quartz, with here and there an atom of blue slaty clay interspersed among the grains. From Jura.
  5. Various specimens of the same, with the clay slate increasing.
  6. The same approaching still nearer to graywacke, with a basis of clay slate, and ultimately terminating in it. These two from Jura.

    These specimens show the transition into common graywacke slate.

  7. The same composition of rock, but in which mica slate holds the place of clay slate.

    Different specimens of this variety demonstrate the passage of quartz rock into that sort of graywacke which I have described under the head of Aberfoyle. From Jura.

  8. The same rocks passing by insensible degrees into a conglomerate, which will by some be ranked with common graywacke. From the same place.

From a comparison of the several characters under which this rock appears in the same place, from the similarity of these characters or of a majority of them in the different situations in which it occurs, there need be no hesitation in concluding that