Page:A Treatise on Geology, volume 1.djvu/282

Of which were found both recent and fossil 426, leaving for the total number of species examined

$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$

7390

The ratio of the species which are both recent and fossil, to the whole number is

$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$

5.7 to 100.0

The 4780 living species consisted
of univalves	$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$	3616	or percent	$\left\{{\begin{matrix}\ \ \end{matrix}}\right.$	75.6
bivalves		1164			24.4
The 3036 tertiary species
univalves	$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$	2098	—————	$\left\{{\begin{matrix}\ \ \end{matrix}}\right.$	60.1
bivalves		938			30.9

Among the shells examined were included 1465 recent, and 259 fossil.

Shells of the land and freshwater, viz.
Freshwater species,	living	bivalves	118	fossil	30
		univalves	151	fossil	151
Land species,	living	univalves	1196	fossil	78

As before observed, the ratio of the number of species, both recent and fossil, to the total number of recent and fossil observed, is

$\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}$

426 to 7390, or, 5.7 to 100

The ratio of the same to the number of recent species, 4780, is	8.9 to 100
And to the number of fossil species, 3036, is	14.0 to 100

But this last general average of the number of tertiary species now living, is composed of many very different ratios, by the study of which M. Deshayes has been led to class the tertiary formations upon a new principle. He assumes, as a general truth, that those tertiary deposits which contain the greatest proportion of existing species are of the most recent date; and on the contrary, that those in which the ratio of existing species is smallest are the oldest. Applying this principle to the most important localities of tertiary strata, and grouping together those which have the greatest agreements in ratio of living species, he arrives at the following series of three terms for the whole mass of tertiary strata.

Localities.
Upper or most recent group.	$\left\{{\begin{matrix}\ \ \end{matrix}}\right.$	Sicily; the subapennine beds; the crag. (Perpignan and the Morea agree in their fossils with the subapennine beds.