350 ON THE APPARENT DISLOCATIONS [Ch. XV. 



mineralogically from true granite. If this state of things be 

 dependent upon the heat to which these strata have been sub- 

 jected, how came it to pass that the angular portions of gneiss 

 could have escaped fusion and an assimilation to perfect gra- 

 nite, when placed not only in contact with, but absolutely 

 enveloped in a mass of melted granite ? In like manner, how 

 could the clay-slate preserve its identity, when we are taught 

 that it is converted into hornblende-schist by exposure to an 

 elevated temperature ? 



We will not, however, enlarge on this topic : many other 

 inferences are so obvious that they will readily suggest them- 

 selves : it remains to know whether these objections can be 

 satisfactorily explained. 



To return to the granite-veins. Do they always proceed 

 from the granite, gradually tapering away in such a manner 

 as fissures might be expected to do if produced by the forcible 

 protrusion of a large mass through the stratified rock ? It 

 has been stated that they exhibit no uniformity either in their 

 size or mode of arrangement ; they proceed from the granite 

 in every direction, underlie at every angle, and, in their 

 course, become larger and smaller in the most disorderly 

 manner; and not only so, but even when comparatively 

 regular, and a foot in thickness, they are often found to 

 terminate in minute strings before they reach the exposed 

 part of the mass from which other veins are given out. These 

 veins also may be frequently seen, not only in the granite, 

 but also near the junction, and even in the slate entirely, at 

 a considerable distance from the granite, varying both in 

 length and thickness, and terminating at both ends either 

 abruptly, or gradually diminishing to a mere thread. When 

 veins of this description occur wholly in the schistose rock, 

 far removed from the granite, they can scarcely be supposed 

 to have proceeded from the latter: thus, the innumerable 

 granite-veins that are completely enveloped in gneiss and 

 mica-slate, could not possibly have had such an origin ; nor 

 the short venous portions and irregular masses of granite 



