Br. Mac Culloch on Quartz Rock, 483 



bF purple and of white quartz, the pebbles being from half an inch 

 to two inches in diameter. In Jura, forming part of the series of 

 the purer quartz rock. 



27. A brecciated mass of felspar and quartz of various colours, 

 compacted by a cement of transparent quartz, forming part of the 

 series at Balahulish. 



28. Specimens from Arisaig, from Assynt, Mar, Balahulish, 

 Airds, Sky, Schihallien, and numerous other places, which consist 

 of variable mixtures of reddish felspar, and transparent quartz, some- 

 times appearing to be nearly all quartz, and at others to contain 

 a large proportion of felspar. The grains are of various dimen- 

 sions, and the texture of the stone is consequently various. At times 

 it has the aspect of a fine reddish sandstone, at others of a coarse 

 grit ; and where the grains are very unequal in dimensions it resem- 

 bles a breccia. The grains have never a defined form. 



•29. A rock consisting of narrow and alternating parallel layers, 

 of fine and coarse granular quartz. Large grains of felspar are 

 found in the coarse layer, but none at all in the fine one. From Ba- 

 lahulish, 



SO. A scarcely coherent combination of large grains of quartz 

 and felspar, the interstices either empty or filled with clay. Part of 

 the series at Balahulish. 



31. Compact extremely fine granular splintery quartz, alternating 

 in thin layers with clay slate. From Cowal. 



32. Fine sandstones, not to be distinguished from the flcetz 

 ■sandstones, and like many of them striped in endless alternations by 

 black clay. From the series of Balahulish. These belong to that 

 •quartz rock which alternates with clay slate, and show the transitions 

 between those two substances. 



^ii. Fine grained granular quartz, alternating with layers of 



3 p 3 



