356 AFFINITIES OF EXTINCT SPECIES. 



general parallelism between the successive stages in the 

 two countries ; but when he compares certain stages in 

 England with those in France, although he finds in both a 

 curious accordance in the numbers of the species belonging 

 to the same genera, yet the species tJiemselves differ in a 

 manner very difficult to account for considering the prox- 

 imity of the two areas, unless, indeed, it be assumed that 

 an isthmus separated two seas inhabited by distinct, but 

 contemporaneous faunas. Lyell has made similar obser- 

 vations on some of the later tertiary formations. Barrande, 

 also, shows that there is a striking general parallelism in the 

 successive Silurian deposits of Bohemia and Scandinavia ; 

 nevertheless he finds a suprising amount of difference 

 in the species. If the several formations in these regions 

 have not been deposited during the same exact periods 

 — a formation in one region often corresponding v*dth a 

 blank interval in the other — and if in both regions the 

 species have gone on slowly changing during the accumu- 

 lation of the several formations and during the long inter- 

 vals of time between them ; in this case the several 

 formations in the two regions could be arranged in the 

 same order, in accordance with the general succession of 

 the forms of life, and the order would falsely appear to be 

 strictly parallel ; nevertheless the species would not be 

 all the same in the apparently corresponding stages in the 

 two regions. 



ox THE AFFINITIES OF EXTIXCT SPECIES TO EACH OTHER, 



AND TO LIVING FORMS. 



Let ns now look to the mutual affinities of extinct and 

 living species. All fall into a few grand classes ; and this 

 fact is at once explained on the principle of descent. 

 The more ancient any form is, the more, as a general 

 rule, it differs from living forms. But, as Buckland long 

 ago remarked, extinct species can all be classed either in 

 still existing groups, or between them. That the extinct 

 forms of life help to fill up the intervals between existing 

 genera, families and orders, is certainly true; but as this 

 statement has often been is^nored or even denied, it mav 

 be well to make some remarks on this subject, and to give 

 Bome instances. If we confine our attention either to the 



