Dall's Tertiary Fauna of Florida. — Schuchcrt. 147 
that has been done during the studies lor this Memoir. Another feature 
which has aroused some comment has been the development of our 
knowledge of the marine strata which in Florida and its vicinity cor- 
respond to the epoch which in Europe has come to be called and recog- 
nized, after Beyrich, as the Oligocene. 
■'Lyell and Deshayes in dividing the Tertiary into periods used the 
percentage of living forms as a criterion, adopting the term Eocene for 
beds containing three to four per cent, of species surviving to the present 
day, — Miocene for those containing from seventeen to twenty per cent., 
and Pliocene for those of which forty to fifty per cent, survive. There 
are several objections to this method of classification, considered as indi- 
cating contemporaneity for the strata concerned ; the view of species 
taken by different persons is by no means uniform; the conditions in one 
region may be more favorable for surviving than in another region at the 
same time, and the method as stated takes no account of changes of cli- 
mate or earth movements on a large scale, to which fluctuations in the 
rate of evolution of living beings must more or less directly conform. 
However, in practice, the omissions have been more or less effectively 
supplied, and the European time column having been thus worked out, 
the establishment of synchronism in the scale of other countries, neces- 
sarily an approximation only, will be none the less useful because to a 
certain extent arbitrary. 
'"According to De Lapparent* European geologists are now pretty 
much agreed in recognizing two great divisions of the Tertiary: i, the 
EoGENE system, divided into Eoc'eiie and Oligocene series, corresponding 
to a state of things still very different both geographically and faunally 
from the present epoch, and especially including all the Nummulitic 
formations ; 2, the Neocene inaugurated in Europe by a great movement 
of transgression, bringing in, with the flexures of the Alps, conditions 
resulting in organic transformations leading to the existing fauna and 
flora. In its turn this system is divided into the Miocene and Pliocene 
series. 
"The Eocene series in Europe terminated by the great earth move- 
ments which uplifted the Pyrenees and Appenines and which were ac- 
companied by a recession of the sea at many points on the shores of 
northern and western Europe. 
"On the Gulf and southeast Atlantic coast of North America no 
marked stratigraphic break has been established between the Eocene and 
Oligocene series. As the studies of the Eocene in this country have 
chiefly been made in this region, it is not surprising that most American 
geologists have been prone to minimize the distinctions between the 
Eocene and Oligocene series. Nevertheless, if the invertebrate fauna is 
taken into account and all allowances made for the existence of a few 
indications of transition, the change in the fauna is so marked that 
physical changes elsewhere must be assumed to account for it, since no 
other hypothesis has even been proposed. The parallelism between the 
Eocene faunas of Europe and North America is so close that no ground 
• Traite de Geologic, ed. iv.. p. 14-09, 1900. 
