Iviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



which the system of the Jura is composed are not exactly in the di- 

 rection of the system itself, hut ohhque in such a maimer as to be 

 parallel with the cham of the Alps." There is in fact an intimate 

 relation between the two chains, and M. Guyot conceiyes that the 

 moyement has been the result of a contraction of the terrestrial sur- 

 face in consequence of gradual cooling, and that the folding has been 

 due to lateral pressure resulting from this contraction. 



It is not my purpose to enlarge at present on the riyal theories 

 thus brought forward to soke a most difficult problem ; and I con- 

 fess myself unable at present to understand how, according to the 

 hypothesis of Mr. Rogers, the grand flexm'es of the strata in moun- 

 tain-chains can bear any intimate relation to great wayes propagated 

 thi'ough a subjacent reserroir of fluid matter. But if M. Guyot be 

 correct in contending that a sinking-down of strata by grayity, owing 

 to a slow contraction of part of the earth's crust below, can explain 

 the flexures, we haye then a cause introduced which might act as in- 

 sensibly as the failure of support, so often witnessed in mines, espe- 

 cially after the remoyal of seams of coal. Such failure giyes rise to 

 what the miners call " creeps," which clearly proye that the sharpest 

 bends and curratures of yielding strata may be brought about by im- 

 perceptible degrees. Eyen if such an hypothesis be entitled, on pure 

 mechanical piinciples, to equal fayour, it should be prefeiTed to one 

 which appeals to extraordinary yiolence, for it must then be admitted 

 that the '* dignus vindice nodus'"^ has not yet occurred. 



I haye already suggested that the talcose or protogene granites of 

 the Alps may belong to the tertiary period. M. de Beaumont be- 

 lieves that they were not protruded into the atmosphere till they had 

 already reached the region of perpetual 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 haye been soHdified at a consi- 

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

 to haye been adyanced to proye that they ought to be regarded, as 

 the French geologist seems to infer, almost as superficial products*. 

 The limestones, sandstones and shales of the nummuhtic and flysch 

 series are of such enormous thickness, that tertiary gi-anites may 

 well be supposed to haye crystallized beneath them, and then to 

 haye been exposed to yiew by breaking forth or bursting through 

 * BuUetin, 2nd Series, vol. iv. p. 1299. 



