350 RELATIVE ANTIQUITY [Ch. XXIV. 



may have been formed in some part of the Eocene period, an 

 hypothesis which does not involve the theory of their having 

 been due to paroxysmal convulsions during one part of that vast 

 period. 



It should be observed, that as some trains of burning vol- 

 canos are parallel to each other, so at all periods some inde- 

 pendent lines of elevation may be parallel accidentally, or not 

 in obedience to any known law of parallelism ; but, on the 

 contrary, as exceptions to the general rule. We hope that 

 the speculations of M. de Beaumont will be useful in inducing 

 geologists to inquire how far the uniformity in the direction 

 of the beds, in a region which has been agitated at any parti- 

 cular period, may extend ; but we trust that travellers will not 

 be led away with the idea that, on arriving in India, America, 

 or New Holland, they have only to use the compass and 

 examine the strike of the beds in order to discover the rela- 

 tive era of the movement by which they were upraised. Such 

 problems can in truth be only solved by a patient and laborious 

 investigation of the sedimentary formations occurring in each 

 region, and especially by the study of their organic remains. 



Difficulties attending the determination of the relative age of 

 mountains. If we are asked whether we cherish no expec- 

 tation of fixing a chronological succession of epochs of elevation 

 of different mountain-chains, we reply, that in the present state 

 of our science we have no hope of making more than a loose 

 approximation to such a result. The difficulty depends chiefly 

 on the broken and interrupted nature of the series of sedimen- 

 tary formations hitherto brought to light, which appears so 

 imperfect that we can rarely be sure that the memorials of some 

 great interval of time are not wanting between two groups now 

 classed as consecutive. Another great source of ambiguity 

 arises from the small progress which we have yet made in iden- 

 tifying strata in countries somewhat distant from each other. 



There may be instances where the same set of strata, pre- 

 serving throughout a perfect identity of mineral character, may 

 be traced continuously from the flanks of one independent 



