d-34 AFFINITIES OF EXTINCT SPECIES. 



I suspect that cases of this nature occur in Europe. 

 Mr. Prestwich, in his admirable Memoirs on the eocene 

 deposits of England and France, is able to draw a close 

 general parallelism between the successive stages in the 

 two countries ; but when he compares certain stages in 

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

 curious accordance in the numbers of the species belonging 

 to the same genera, yet the species themselves 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 observa- 

 tions 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 surprising amount of difference in 

 the species. If the several formations in these regions have 

 not been deposited during the same exact periods — a forma- 

 tion in one region often corresponding with a blank interval 

 in the other — and if in both regions the species have gone 

 on slowly changing during the accumulation of the several 

 formations and during the long intervals 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. 



OK THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER, 



AND TO LIVING FORMS. 



Let us 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 ignored or even denied, it may 

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

 gome instances. If we confine our attention either to th$ 



