Ch. XV.] OF THE PRIMARY ROCKS. 335 



by the contact of melted granite ; the protrusion or lateral 

 extension of which is the adopted cause of the bendings and 

 flexures of the gneiss and mica-slate. Now, without stopping 

 to enquire which mode of motion is the more probable, 

 whether that previous to, or that attendant on, the elevation 

 of these strata from a horizontal to their present elevated 

 inclination, let it be admitted that these concurrent con- 

 ditions of plasticity and motion (which we have already 

 contested) have effected the curvatures of these rocks. If 

 this be the case, how then has it happened that one stratum, 

 or a series of strata, is regularly curved at one point, and yet 

 is broken off abruptly at another ; or, to speak more cor- 

 rectly, terminates abruptly. This is of frequent occurrence ; 

 but, what is more to the purpose, the apparent fracture and 

 flexure may be sometimes witnessed at the same point of 

 curvature ; several examples of which have been recorded by 

 Macculloch, but one remarkable instance, in particular, 

 which he saw in Lunga, one of the Western Isles of Scotland, 

 and which he has attributed to the modified action of the 

 moving power, operating on strata of a different nature, the 

 associated rocks consisting of alternating layers of argillaceous 

 schist and quartz- rock. " Where the flexure is very acute, 

 the quartz-rock is broken, while the schist is only bent; and, 

 in some extreme cases, fragments of the former are separated 

 and entangled among the latter; facts speaking a language 

 that cannot be misapprehended." * A different view, how- 

 ever, may be taken of this phenomenon, and it may be 

 interpreted into evidence unfavourable to the conditions of 

 plasticity and motion ; for if the whole were softened, how 

 came it to pass that the quartz -rock was " urged beyond its 

 power of flexibility ? " Because, it may be answered, the 

 quartz-rock and the argillaceous schist possessed different 

 degrees of hardness. But this is a mere assertion ; we do 

 not know that the latter is more fusible than the former, on 



* System of Geology, vol. i. p. 115. 



