836 STRATIGRAPHICAL GEOLOGY. [Boox VI. 
the two periods. ‘The one merged insensibly into the other; but 
the strata which would have served as the chronicles of the inter- 
vening ages have either never been deposited or have since been in 
great measure destroyed. In southern Europe, and especially in the 
south-eastern Alps, no sharp line can be drawn between Cretaceous 
and Kocene rocks. These deposits merge into each other in such 
a way as to show that the geographical changes of the western 
region did not extend into the south and south-east. 
The name Tertiary, given in the early days of geology before 
much was known regarding fossils and their history, has retained its 
hold on the literature of the science. It is often replaced by the 
term Cainozoic (recent life), which expresses the great fact that it is 
in the series of strata comprised under this designation that most 
recent species and genera have their earliest representatives. ‘Taking 
as the basis of classification the percentage of living species of mol- 
lusca found by Deshayes in the different groups of the Tertiary 
series, Lyell proposed a scheme of arrangement which has been 
generally adopted. The older Tertiary formations, in which the 
number of still living species of shells is very small, he named Hocene 
(dawn of the recent), including under that title those parts of the 
‘Tertiary series of the London and Paris basins wherein the propor- 
tion of existing species of shells was only 34 per cent. The middle 
Tertiary beds in the valleys of the Loire, Garonne, and Dordogne, 
containing 17 per cent. of living species, were termed Miocene (less 
recent), that is, containing a minority of recent forms. The younger 
Tertiary formations of Italy were included under the designation 
Pliocene (more recent), because they contained a majority, or from 
36 to 95 per cent., of living species.” This newest series, however, 
was further subdivided into Older Pliocene (85 to 50 per cent. of 
living species) and Newer Pliocene (90 to 95 per cent.). A still 
later group of deposits was termed Pleistocene (most recent), where 
the shells all belonged to living species, but the mammals were 
partly extinct forms. This classification, though somewhat artificial, 
has, with various modifications and amplifications, been adopted for 
the Tertiary groups, not of Europe only, but of the whole globe. 
The original percentages, however, often depending on local acci- 
dents, have not been very strictly adhered to. ‘The most important 
modification of the terminology in Europe has been the insertion of 
another stage or group termed Oligocene, proposed by beyrich, to 
include beds that were formerly classed partly as Upper Eocene 
and partly as Lower Miocene. 
Some writers, recognizing a broad distinction between older and ~ 
younger Tertiary deposits, have proposed a classification into two 
main groups: Ist, Hocene, Older Tertiary or Paleogene, including 
Eocene and Oligocene; and 2nd, Younger Tertiary or Neogene. 
This subdivision has been advocated on the ground that while the 
older deposits indicate a tropical climate and contain only a very 
few living species of organisms, the younger groups point toa climate 
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