CH. XV.] OF THE PRIMARY ROCKS. 34-1 



nected, if not identical with, the spheroidal structure so 

 generally observed to prevail in granite, and in the various 

 porphyries and traps. It is not always very evident, but is 

 generally developed in the individual concretions of these 

 rocks by disintegration ; and is often conspicuous on a large 

 scale, in the round-backed form of hills which are entirely 

 composed of such rocks. 



Now some may contend, that even these appearances may 

 have been produced by force applied to these rocks whilst 

 in a state of semi-fusion. If, however, any power has in- 

 fluenced this arrangement, it is probably only such as might 

 arise from the expansion and movement of the parts during 

 crystallisation or consolidation ; a force very different from 

 that which is supposed to have deranged the laminae and 

 strata of the sedimentary rocks. 



On all these considerations, therefore, it may be concluded, 

 that the various curved appearances which rocks present, are 

 not certain indications of their having been subjected to 

 mechanical violence ; on the contrary, that they are not 

 incompatible with the effects of the power of cohesion by 

 which the rocks were consolidated. 



This opinion has been entertained by many geologists ; and 

 amongst others, by Mr. Weaver, who, after a careful examin- 

 ation of the inflections and contortions of the rocks in the 

 east of Ireland, considers that these peculiar arrangements 

 have not been produced by violence; and concludes, that 

 these appearances, as well as the stratified structure, in all its 

 varieties, result from concretion on the large scale.* 



The spheroidal structure brings us to the consideration of 

 the brecciated and conglomerated appearance of some rocks, 

 which have by many geologists been regarded as sure 

 evidence of a mechanical origin. 



It must not for a moment be imagined, that we are about 

 to contend that all breccias and conglomerates are not frag- 



* Geol. Trans, vol. v. p. 175. 

 Z 3 



