Dr. ^iAC CuLLOCH on Qiiarl% Rock. 4-85 



quartz rock wherever occurring is generlcally the same, and that It 

 differs no more from Itself than the numerous varieties of gneiss, 

 of mica slate, or of graywacke are found to do. It ought therefore to 

 be designated in a geological system by one general name, since, as the 

 designations of rocks are Intended for the purposes of geology, rather 

 ' than of mineralogy, ii is preferable that one common term should be 

 applied to the rock in question, than that the several varieties should 

 each receive a separate one, a circumstance tending as much to con- 

 fuse geological reasonings, as to render them tedious and intricate. 

 It has already received various names, out of which it would be desi- 

 rable to agree on one. It has been called granular quartz, transition 

 sandstone, quartzose graywacke, and quartz rock. The first of these 

 sufficiently expresses the character of one of its varieties ; but its par- 

 ticularity excluding those modifications which are not granular, as well 

 as those which contain felspar, is not well adapted for the purposes of 

 geological description. Could we prove that it was In every case a rock' 

 of transition, and that the theory which the term transition implies 

 was well founded, the name of transition sandstone would perhaps 

 be the most applicable. But as I have ascertained that it alternates 

 at times with rocks, which the system here alluded to calls primitive, 

 and as it is at all times desirable to keep clear of those terms which 

 involve an hypothesis, I think we are bound to reject this name. 

 The same argument is valid against the appellation of quartzose 

 graywacke, a term in other respects perfectly inapplicable, since the 

 very definition of graywacke decidedly excludes it ; and there can 

 be no greater evil than to confound under one name, substances of dif- 

 ferent qualities, particularly when that name itself, from its con- 

 nection with an hypothesis, tends to blind our judgment and per- 

 vert our reasonings. I should therefore suggest the superior propriety 

 of the term quartzy or quartz rock, a term involving no hypothesis, 

 and which, at the same time that it is sufficiently general to include 



