Ch. XXIV.] 
OF MOUNTAIN-CHAINS. 
343 
western end of the Pyrenees, near Bayonne, are certainly of 
the Miocene period. 
Such, then, being the age of the strata, and granting even 
that the movement occurred after the period of the white 
chalk, and before the beginning of the Miocene era, there still 
remains ample scope for conjecture as to the date of the event. 
For the upheaving of the Pyrenees may have been going on 
when the animals of the Maestricht beds flourished, or during 
the indefinite ages which may have elapsed between their ex- 
tinction and the introduction of the Eocene tribes, or during 
the Eocene epoch, or between that and the Miocene. Or the 
rise may have been going on continuously throughout several 
or all of these periods. 
But this is not all ; we must include within the possible space 
of time wherein the convulsions may have happened, part of the 
epochs both of the chalk and of the Miocene species. We have 
stated, that the newer Pliocene beds in Sicily have been raised 
during the newer Pliocene epoch, partly, perhaps, in the 
Becent, but this latter supposition will lend equal support to 
our present argument. Now, it is evident that the greater part 
of the species of testacea which pre-existed in the Mediterranean 
have survived the elevation of the newer Pliocene beds in 
Sicily, and in the same manner there is no reason to conclude 
that the rise of the chalk in the Pyrenees exterminated the 
animals which lived in the sea wherein the chalk was formed. 
In that case, a series of convulsions may not only have begun, 
but may even have been completed before the era when the 
Maestricht beds originated. 
In like manner the sea may have been inhabited by Miocene 
testacea for ages before the deposition of those particular 
Miocene strata which occur at the foot of the Pyrenees, and 
the disturbing forces may have operated in the Miocene period, 
from the newest secondary beds on the flanks of the Pyrenees, near Bayonne, were 
examined by M. Deshayes, and found identical with species of the chalk near 
Paris. 
