





* 





fc 









q aft 





u„ 



fi 





irk 



•bt 



' 





• 





1 -.* 



i 









Ch. VII.] 



PAEALLEL MOUNTAIN-CHAINS. 



125 



whether the inclined and undisturbed sets of strata in each 

 range correspond with or differ from those in the typical 



chains A and B. 



Now all this reasoning is perfectly correct, so long as the 

 period of time required for the deposition of the strata b and 

 c is not made identical in duration with the period of time 

 during which the animals and plants found fossil in b and c 

 may have flourished ; for the latter, that is to say, the dura- 

 tion of certain groups of species, may have greatly exceeded, 

 and probably did greatly exceed, the former, or the time 

 required for the accumulation of certain local deposits, such 

 as b and c (figs. 1 and 2). In order, moreover, to render 

 the reasoning correct, due latitude must be given to the 

 term contemporaneous ; for this term must be understood to 

 allude, not to a moment of time, but to the interval, whether 

 brief or protracted, which elapsed between two events, namely, 

 between the accumulation of the inclined and that of the 

 horizontal strata. 



But, unfortunately, no attempt has been made in the 

 treatises under review to avoid this manifest source of con- 

 fusion, and hence the very terms of each proposition are 

 equivocal ; and the possible length of some of the intervals 

 is so vast, that to affirm that all the chains raised in such 

 intervals were contemporaneous is an abuse of language. 



In order to illustrate this argument, I shall select the 

 Pyrenees as an example. Originally M. E. de Beaumont spoke 

 of this range of mountains as having been uplifted suddenly 

 (a un sent jet), but he has since conceded that in this chain, 

 in spite of the general unity and simplicity of its structure, 

 six, if not seven, systems of dislocation of different dates 

 can be recognised.* In reference, however, to the latest, 



and by 



most 



these convulsions, the 



chain is said to have attained its present elevation at a cer- 



nam 



sition of the chalk, or rocks of about that age, and that of 

 certain tertiary formations ' as old as the plastic clay ; 5 for 

 the chalk is seen in vertical, curved, and distorted beds on 

 the flanks of the chain, as the beds 6, fig. 1, while the tertiary 



* Systemes de Montagnes, 1852, p. 429. 



