y3 GRANITE. 



so that it becomes granitic ; from chemical changes 

 which I must shortly proceed to notice. 



In the vicinity, as well as at the contact of the 

 veins, the strata are generally broken and diverted 

 from their otherwise even position, while fragments of 

 them are often also found detached and insulated 

 among the intersections ; gneiss, in this case, being 

 sometimes so placed and extenuated, as itself, to put 

 on the fallacious appearance of veins. Even the pro- 

 trusive force of the Vein is often indicated in the 

 averted direction of the edges of the strata in contact ; 

 while the variety of the appearances marking violence, 

 however demonstrative of the nature of the actions 

 which produced them, need not now be repeated. I 

 must not however omit the formation of conglomerates 

 from the invaded rock, at these poiuts; a circumstance 

 equally occurring, like every other one. at the junc- 

 tions of Trap. 



The chemical changes of the strata at these points 

 are often such, and so extensive, as to have rendered 

 it necessary to enumerate some of the rocks so in- 

 fluenced, under separate titles from those whence 

 they have been thus produced. Gneiss thus becomes 

 converted from the schistose to the granitic character 

 in almost every case ; clay slate into siliceous schist 

 very widely and generally, and, into hornblende schist, 

 in a more limited manner, though sometimes very 

 extensively, as in Shetland. The entangled frag- 

 ments are also often changed into the same substance ; 

 while the cause becomes demonstrated by tracing the 

 gradual nature of that change where the continuity is 

 uninterrupted. In the same situations, quartz rock 

 is indurated to a crystalline texture and hardness ; 

 and, when containing felspar, it becomes jasper, as 

 in Ben na chie. It is repeating former general state- 



