60 Dr, M<=Culloch's Supplementary Remarks on Quart'^ Rock. 



Quartz Rock is 



Simple, or formed of quartz alone. 



a. Compact, and resembling- that which occurs in veins. 

 6. Compact, and, at the same time, obscurely granular. 



c. Compact, with a small splintery fracture. 



d. Granular, with grains of various sizes, and highly compacted. 



e. Granular, and more or less loose, so as to resemble the secondary sand- 



stones. 

 d. Laminar ; often slightly schistose. 



Compounded — of quartz and felspar. 



a. Grains of felspar imbedded in compact quartz. 



b. A granular mixture of various proportions of these two minerals. This 



variety presents some modifications similar to the preceding, on which 

 it is unnecessary to dilate. ^ 



Compounded — of quartz and mica. 



a. Mica imbedded in quartz. 



b. An arenaceous mixture of the two. 



c. A laminar mixture ; of various aspects, and passing to micaceous schist. 



Compounded — of quartz and argillaceous schist. 



a. A laminar alternation of the two substances on a more or less distinct 



scale. 



b. Argillaceous schist uniting grains of quartz, and thus passing into gray- 



wacke. 



Conglomerate quartz rock. 



This presents many varieties ; the fragments of quartz being either angular 

 or rounded, of various sizes, and intermixed with mica and schistose blue clay, 

 and with fragments of argillaceous and of micaceous schists, and even of jasper. 

 These pass into coarse schists, resembling the graywackes of similar character. 



Quartz rock has not hitherto been found to contain any imbedded minerals, 

 except pyrites and garnet. 



