30 Anniversary/ Address of the 



steep, short dips do not face the crystalline nucleus, but the 

 longer and less inclined ones, except where a curve has been 

 so great that the whole are made to dip one way, the more 

 steeply inclined side having become, as it were, more than 

 vertical. 



In the Alps, the anticlinal folds, where they are greatest, 

 dip inwardly towards the central peaks, and therefore in 

 opposite directions on each flank of the chain. In the Jura, 

 the steep, sharp dips of each parallel fold are upon the side, 

 facing the Alps, and hence Professor Rogers imagines that 

 the subterranean undulations in the earth's crust, which, ac- 

 cording to his theory, gave rise to these flexures, were pro- 

 pagated, not from the Alps, but from the district of the 

 Vosges, or the country towards the north-west. To this 

 theory Professor A. Guyot strongly objects, arguing that it 

 is more probable, on the contrary, that the immediate cause 

 of the uplifting of the Jura is to be sought in the upheaval 

 of the Alps. " The elevation," he remarks, " of the anti- 

 clinal ridges of the Jura diminishes gradually and regularly 

 in proportion as the Jura recedes from the Alps, the summits 

 sinking from 5000 to 2000 feet. The minor chains also of 

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

 the direction of the system itself, but oblique in such a man- 

 ner as to be parallel with the chain of the Alps." There is 

 in fact an intimate relation between the two chains, and M. 

 Guyot conceives that the movement has been the result of a 

 contraction of the terrestrial surface in consequence of gra- 

 dual 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 rival 

 theories thus brought forward to solve a most difficult pro- 

 blem ; and I confess myself unable at present to understand 

 how, according to the hypothesis of Mr Rogers, the grand 

 flexures of the strata in mountain-chains can bear any in- 

 timate relation to great waves propagated through a sub- 

 jacent reservoir of fluid matter. But if M. Guyot be correct 

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

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

 explain the flexures, we have then a cause introduced which 



