209 
CHAPTER XL 
FOREIGN EQUIVALENTS OF THE ENGLISH 
PLIOCENE STRATA. 
The study of any group of strata exclusively from the stand¬ 
point of a single limited area like Britain is likely to lead to 
wrong conclusions as to the real importance of each strati- 
graphical division, inasmuch as it proceeds on too narrow a basis 
and tends to blind us to the great imperfection of the record, and 
allows us to forget the fundamental truth that a gap in the 
strata, marked only by a line, may represent a longer period 
than the whole of the deposits that are now preserved. Espe¬ 
cially is this the case when we study a group of shallow-water 
strata like the British Pliocene deposits, which in no one locality 
reach a thickness of 200 feet. When we think of the meaning 
of this small development the reason becomes obvious—the 
Upper Pliocene strata were deposited in such shoal water that 
no increase of thickness was possible, though the sediments were 
constantly being scoured out and redeposited. On the further 
side of the North Sea there is a great expansion of these 
deposits, for there, instead of a stationary area there was one of 
subsidence. We scarcely realise the true importance of the 
Pliocene period, however, till we see the enormous mass of the 
8ub-Apennine strata of Italy, and observe how large an area 
they cover. 
It was felt that this Memoir would be made more complete 
by an examination of the corresponding deposits in other 
countries. There is great advantage also in being able to meet 
other observers, who look at things from a somewhat different 
point of view. And, lastly, the study of the fossils in foreign 
museums will often show that whole groups of species appearing 
under different names are merely somewhat modified represen¬ 
tatives of well-known forms. In fact they are old geographical 
races, which are called species or varieties according to the 
personal bias of different observers. 
During the spring of 1886 I had made a holiday visit to 
Auvergne and the south of France, for the purpose of examining 
the Pliocene strata ; but the limited time at my disposal rendered 
it impossible to go further. Soon after I was delegated by the 
Director General to make the necessary journeys, and spent 
three weeks in Belgiu[n, in company with Messrs. Van den 
Broeck, Cogels, and Van Ertborn. Opportunity was at the 
game time taken to visit Utrecht to meet Dr. J. Lorie and to 
examine the original specimens obtained from the deep borings 
E 60798. O 
