President of the Geological Society for 1850. 31 



might act as insensibly as the failure of support, so often 

 witnessed in mines, especially after the removal of seams of 

 coal. Such failure gives rise to what the miners call " creeps,'* 

 which clearly prove that the sharpest bends and curvatures 

 of yielding strata may be brought about by imperceptible 

 degrees. Even if such an hypothesis be entitled, on pure 

 mechanical principles, to equal favour, it should be preferred 

 to one which appeals to extraordinary violence, for it must 

 then be admitted, that the " dignus vindice nodus'^ has not yet 

 occurred. 



I have already suggested that the talcose or protogene 

 granites of the Alps may belong to the tertiary period. M. 

 de Beaumont believes that they were not protruded into the 

 atmosphere till they had already reached the region of per- 

 petual snow. Whether there may be good grounds for such 

 an opinion or not, it does not appear to me to follow that 

 such granites may not have been solidified at a considerable 

 depth in the bowels of the earth. No sufficient reason seems 

 to have been advanced to prove that they ought to be regarded, 

 as the French geologist seems to infer, almost as superficial 

 products.* The limestones, sandstones, and shales of the 

 nummulitic and flysch series are of such enormous thickness, 

 that tertiary granites may well be supposed to have crystal- 

 lized beneath them, and then to have been exposed to view 

 by breaking forth or bursting through the covering of sedi- 

 mentary matter in the course of the enormous change of 

 position which the Alpine eocene rocks have undergone. The 

 question is one of the highest importance, because the French 

 academician contends, that all the granites erupted in the 

 earlier periods of the earth's history difi^ered from those of 

 later date, in being much more quartziferous ; and he contro- 

 verts the doctrine proposed by me in my *' Elements of Geo- 

 logy," that the difference of mineral composition in the oldest 

 rocks of this class now visible may reasonably and naturally 

 be explained by imagining them to have originated at a great 

 depth below the surface. On the contrary, M. de Beaumont 

 supposes that granitic rocks charged with an excess of silice- 



* Bulletin, 2d Series, vol. iv. p. 1299. 



