6 



ON COTEMPORANEOUS VEINS. 



these veins in general do not extend beyond 

 the individual stratum in which they are con- 

 tained. Transition-limestone is often traversed by 

 cotemporaneous veins of calc-spar, and these 

 veins frequently open on the upper and under 

 sides of individual beds, contained between stra- 

 ta of grey-wacke, and grey- w a eke- s 1 a te . Some- 

 times the matter of these veins is observed mixed 

 with the matter of the subjacent stratum, al- 

 though that stratum be completely different from 

 the limestone or calc-spar. In mountains com- 

 posed of strata of gneiss, veins of felspar, and of 

 quartz, also of simple granular or granitic gneiss, 

 occur in precisely the same situation and rela- 

 tions, as the veins of quartz, and granular mica- 

 slate, in mountains of common mica-slate. It 

 sometimes happens, that cotemporaneous veins of 

 granitic gneiss open on the under-side or floor of 

 a stratum of common gneiss, where it rests upon 

 granite; and such appearances, which are not un- 

 common, have been viewed as veins of granite, 

 shooting from old granite into the superincum- 

 bent gneiss, arid as demonstrating that granite is 

 newer than the rocks which rest upon it #. 



* If granite be really newer than the rocks which rest 

 upon it, it follows, that it must be newer than grey-wacke, 

 transition-trap, transition-limestone, floetz-limestone, and 

 floetz-sandstone, because these rocks have been observed, 

 and in highly inclined strata, resting upon granite ; in shorty 



