ELEVATION OF MOUNTAIN RANGES. 



339 



scattered over Savoy, rolled off from the regions of the higher Alps, 

 during this last period of their elevation. There are six other sup- 

 posed periods of elevation. If these generalizations be true, and 

 they seem to be based on an immovable mass of evidence, we must 

 conclude, that there have been, in the history of the earth, long pe- 

 riods of comparative repose, during which the sedimentary deposits 

 went on in regular continuity ; and short periods of comparative vio- 

 lence and revolution, during which that continuity was broken ; and 

 if we admit that the higher regions of the globe have been raised 

 from the sea by any modification of volcanic force, we must then 

 also admit, that there have been several successive periods of extra- 

 ordinary volcanic energy. How we are to escape from this conclu- 

 sion 1 am unable to comprehend, unless we shut out the evidence of 

 our senses. 



" That the system of M. Elie de Beaumont is directly opposed to 

 a fundamental principle of Mr. Lyell, cannot admit of doubt ; and I 

 have decided in favor of the former author, because his conclusions 

 are not based upon any a priori reasonina;, but on the evidence of 

 facts.*" 



If we admit that the primary, the transition, the secondary, and 

 the tertiary classes of rock, were formed at different successive 

 epochs, and that the lower beds in each of these classes, are more 

 ancient than the beds which rest upon them, it follows, as a neces- 

 sary consequence, that the elevation of any of these rocks, must be 

 dated from a later epoch than the period of their formation. The 

 elevation of a range of primary or transition mountains, if they are 

 not covered by any secondary or tertiary formations, may be dated 

 either from an epoch coeval with their consohdation, or from any 

 subsequent epoch ; but if they are partly covered by secondary or 

 tertiary beds which are tilted up with them, we have direct evidence 

 that the date of their elevation, was posterior to the secondary or 

 tertiary epoch. So far we may advance on secure ground ; but 

 when we infer, that mountains which range in the same direction 

 were all elevated at the same time, we wander into the region of 

 vague hypothesis. It is by no means certain, that the elevation of 

 the outer ranges of the Alps was contemporaneous with that of the 

 principal range. In various part of Savoy, I observed that the 

 mountains at a certain distance from the central range, had their es- 

 carpments turned in a different direction, and frequently took the 

 arched form of stratification, as represented Plate II. fig. 2. a?, y. 



* Though I agree with Professor Sedgwick and M. Elie de Beaumont, that the 

 elevation of mountain ranges, where tiie beds are nearly vertical, was eiFected 

 by a sudden and violent upheaving, yet I am persuaded, that the elevation of con- 

 tinents, or extensive tracts of country, was (as Mr. Lyell maintains) a long con- 

 i tinned process. It may be proved that these operations were distinct from each 

 other, as I shall afterwards state. 



