350 
RELATIVE ANTIQUITY 
[Ch. XXIV. 
may have been formed in some part of the Eocene periods — 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 
