328 
GEOLOGICAL SUCCESSION. 
Chap. X. 
other parts of the world. As we have reason to 
believe that large areas are affected by the same move¬ 
ment, it is probable that strictly contemporaneous for¬ 
mations have often been accumulated over very wide 
spaces in the same quarter of the world; but we are 
far from having any right to conclude that this has in¬ 
variably been the case, and that large areas have invari¬ 
ably been aflected by the same movements. When two 
formations have been deposited in two regions during 
nearly, but not exactly the same period, we should find 
in both, from the causes explained in the foregoing 
paragraphs, the same general succession in the forms of 
life; but the species would not exactly correspond ; for 
there will have been a little more time in the one region 
than in the other for modification, extinction, and im¬ 
migration. 
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 finds 
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 proximity 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 observations 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; never¬ 
theless he finds a surprising amount of difference in 
the species. If the several formations in these re¬ 
gions have not been deposited during the same exact 
