Cb. XV.] OF THE PRIMARY ROCKS. 339 



when this contorted structure occurs in schistose rocks, the 

 laminae are often found to correspond with the flexures, and 

 consequently they are fissile in the same direction. 



It is, therefore, no easy matter to determine where the line 

 is to be drawn between these different kinds of curvatures, so 

 as to separate those which are supposed to have been pro- 

 duced by the application of force to rocks in a soft and ductile 

 state ; for, indeed, they are so connected one with another, 

 and assume such identical forms, that one is a perfect repre- 

 sentation of the other in miniature. 



If this be admitted, another step will lead us to the waved 

 and marbled delineations in agates and alabasters : and then 

 the conclusion irresistibly forces itself on us, that all these 

 internal contortions of every degree and size, whether of the 

 whole or any portion of a rock, may be referred to a peculiar 

 mode of concretionary structure, how difficult soever it may 

 be to conceive by what means it was produced. 



On this view of the subject, the same kind of structure 

 might be expected to occur in granite and other igneous 

 rocks, that is, in the very agents themselves to which the 

 curvatures of the stratified rocks have been attributed : for it 

 has been shown that the same laminated, schistose, and 

 tabular structures, are common to rocks both of igneous and of 

 aqueous origin ; and, if these different modes of structure are 

 independent of the nature of the rock's origin, and only to be 

 ascribed to the modified operations of the attraction of co- 

 hesion, by which the incoherent particles of the rock were 

 consolidated, the igneous rocks ought also to exhibit curves 

 and contortions. And so they do ; this theoretical deduction 

 is borne out by an appeal to nature. Wherever a good sec- 

 tion of granite is exposed in a cliff or quarry, we shall find 

 that the parallel lines by which this rock is intersected, 

 though having a regular bearing, like the curved strata when 

 viewed along a line of considerable extent, are very seldom 

 perfectly straight, but are more or less curved ; and this 

 obtains not only with the horizontal, but also with the per- 



z 2 



