ON THE CARTLANE CRAIG. 



499 



the banks of the Clyde above Lanark. The frag- 

 ments it contains when coarse-grained, are angu- 

 lar pieces and rolled masses, of quartz, felspar, 

 grey-wacke, clay-slate, jasper, flinty-slate, &c., 

 often so large, that some of the beds may be re- 

 garded as conglomerates. But the greater por- 

 tions of the strata are fine granular, composed of 

 quartz, felspar, and mica, minutely aggregated, in 

 some varieties without a base, in others with a 

 cement of clay ; and the mixture is so pure, as to 

 render these varieties excellent specimens of what 

 Professor Jameson is inclined to consider as true 

 chemical depositions. Quartzy-sandstone also oc- 

 curs, with facettes of felspar. 



In this formation, most of the rocks exhibit 

 numerous scales of mica. We find in others, 

 specks of embedded copper-pyrites. Lime, too, 

 frequently appears in the lowest strata, pervading 

 the substance of the rock, as a kind of base, or 

 penetrating it in the form of cotemporaneous calc- 

 spar veins. In the former case, we have what 

 may be called arenaceous limestone, which may 

 be found in the bed of the river above Clyde 

 Bridge. Veins of heavy-spar sometimes occur. 

 The variety of colours in the different strata, seems 

 to depend on the greater or less abundance of iron. 



With regard to the trap-rock, of which the po- 

 sition has been described, its oryctognostic cha- 

 racters do not exhibit much variety. The great- 

 est mass, is a compact greenstone, intermixed with 



