90 TERTIARY SERIES. 
Mammalia of the Miocene Period, 
The second, or Miocene System of Tertiary 
Deposits, contains an admixture of the extinct 
genera of lacustrine mammalia, of the first or 
Eocene series, with the earliest forms of genera 
which exist at the present time. This admix- 
ture was first noticed by M. Desnoyers, in the 
marine formations of the Faluns of Touraine.* 
Although carbonate of lime occurs not in distinct masses 
among rocks of igneous origin, it forms an ingredient of lava 
and basalt, and of various kinds of trap rocks. The calcareous 
matter thus dispersed through the substance of these volcanic 
rocks, seems to afford a magazine from which percolating water, 
charged with carbonic acid gas, may, in the lapse of ages, 
have derived sufficient carbonate of lime to form all the existing 
strata of limestone, by successive precipitates at the bottom of 
ancient lakes and seas. Mr. De la Beche states the quantity 
of lime in granite composed of two-fifths quartz, two-fifths 
felspar, and one-fifth mica, to be 0.37 ; and in greenstone, com- 
posed of equal parts of felspar and hornblende, to be 7.29. 
(Geol. Researches, p. 379.) — The compact lava of Calabria con- 
tains 10. of carbonate of lime, and the basalt of Saxony 9.5. 
We may, in like manner, refer the origin of those large 
quantities of silex, which constitute the chert and flint beds 
of stratified formations, to the waters of hot springs, holding 
siliceous earth in solution, and depositing it on exposure to 
reduced degrees of temperature and pressure, as silex is deposited 
by the hot waters that issue from the geysers of Iceland. 
* Here, the remains of Palaeotherium, Anthracotherium, and 
Lophiodon, which formed the prevailing genera in the Eocene 
period, are found mixed with bones of the Tapir, Mastodon, 
Rhinoceros, Hippopotamus, and Horse : these bones are frac- 
tured and rolled, and sometimes covered with flustra, and must 
have been derived from carcases drifted into an estuary, or sea. 
Annales des Sciences Naturclles. Ftvrier, 1828. 
