340 ELEVATION OF THE PYRENEES, AND OF ARCHED STRATA. 



Indeed, M. Elie de Beaumont has himself been obliged to modify 

 his generalizations considerably, as will appear from the following 

 extract from the Bulletin de la Societe Geologique de France. M. 

 Reboul, in a memoir on the structure of the Pyrenees, read to the 

 society in December, 1831, states, that several distinct axes of ele- 

 vation may be observed in different parts of these extensive moun- 

 tain ranges, inclined in different directions to each other, and that 

 the lines of bearing of the strata are also different in each. There 

 are, he observes, indications in the Pyrenees, of the elevation of 

 rocks at different epochs, both before and after the most recent sec- 

 ondary depositions, that rise to the summit of Mont Perdu. He 

 also states instances of the tertiary beds of molasse, being elevated 

 near the central range of the Pyrenees, whereas in the Alps they 

 occupy only the central parts of the range, which would imply that 

 the period of elevation of that part of the Pyrenees, was more re- 

 cent than that of the Alps. It appears, however, in the same report, 

 that M. Elie de Beaumont now admits four epochs of elevation in the 

 Pyrenees : the most ancient immediately succeeded the formation of 

 the transition rocks. The second took place between the deposition 

 of the green sand, and that of the upper chalk. The third epoch of 

 elevation was posterior to the chalk formation. The fourth, which 

 gave birth to the serpentines, (ophites,) and to the gypsum with rock 

 salt, is more recent than the tertiary epoch. 



M. Beaumont, however, contends, that notwithstanding the four 

 different directions of the ranges in the Pyrenees, of which traces 

 may be observed in several of the valleys, the great chain of the 

 Pyrenees, owes its actual elevation and general direction, to the third 

 system or epoch of elevation, which was posterior to the chalk form- 

 ation ; the two former epochs of elevation, discoverable in this chain, 

 having been modified by the great elevation of this third epoch. 

 The fourth epoch of elevation is only perceivable, in the localities 

 where serpentine rocks appear. 



I wish to press upon the attention of geologists the consideration, 

 that the arched stratification implies a very limited extent of opera- 

 tion. Where it is confined to one mountain, as at Crich Cliff, (see 

 the cut, p. 96.) the elevating force may be said to act at one point. 

 Where the arched stratification extends through a range, it may be 

 said to act along narrow lines, forming mountain ridges, with valleys 

 between them. From what I observed in the Alps, I was convinced 

 that the explosive force which upheaved Mont Blanc, and the cen- 

 tral range of the Alps, did not extend its action very far from the 



* The formation of serpentine (which was formerly considered as a primary- 

 rock) after the tertiary epoch, will cease to surprise geologists,,, since the identity 

 of basalt, green stone, and serpentine, has been ascertained by Dr. Macculloch. 

 Serpentine, like basalt and volcanic rocks, may have been formed among any 

 class of rocks. It was stated in Chapter XL, that some of the rock salt deposits 

 in Poland were in tertiary strata. 



