TERTIARY FORMATIONS. 109 
highly interesting character of the tertiary strata began to be ap- 
preciated and understood. Those occupying the Paris basin were 
represented by these philosophers as admitting of four great di- 
visions, and these of certain smaller subdivisions. 
1. Immediately upon the chalk reposes a stratum of marine 
origin, with some intermixture of freshwater beds. The most 
important member of this division is a coarse limestone, abound- 
ing in shells, in excellent preservation. It is about ninety feet in 
thickness, and as some parts of it afford a building stone of good 
quality, numerous quarries have been opened in it beneath and 
around the city of Paris. 
2. Next in order, is a freshwater formation, consisting of beds 
of gypsum and gypseous marl. It is remarkable chiefly as con- 
taining near its upper surface, the remains of several genera and 
species of Mammalia that no longer exist upon the surface of the 
globe, the successful study and determination of which have im- 
mortalized the name of Cuvier. 
3. There succeeds a stratum of sandstone, the lower beds of 
which are without organized remains of any kind, but those high- 
er up, abound in shells belonging to races that inhabit the sea. 
4. Covering all these is a second freshwater formation of very 
variable mineralogical character, presenting in some parts a soft 
friable limestone, and in others the hardest siliceous minerals, as 
jasper and buhr millstone. 
The order of superposition of these deposits was represented to 
be such as has just been stated, but they all rise to the surface in 
places, as along their edges, or where they have been laid bare by 
the removal of the mass of material lying above. The shells had 
been previously studied and illustrated with wonderful zeal and 
ability by Lamarck ; the bones of the Mammalia attracted the at- 
tention of Cuvier about the year 1S00, and gave origin to the in- 
vestigation by Cuvier and Brongniart, the results of which have 
just been exhibited. Succeeding observers have proposed some 
modifications of the scheme of classification, especially in the first 
and second of these assemblages of strata, which are now sup- 
posed to have been nearly contemporaneous. 
As the investigations just noticed, were conducted with great 
skill and ability, and the published report of them was very full, 
filling nearly 300 quarto pages, the strata of the Paris basin be- 
came a sort of standard to which other strata bearing any resem- 
blance to them, discovered in other countries, were referred. 
Such strata exist in England, on both sides of the Thames, above 
and below London , and upon the Isle of Wight and in its neighbor- 
hood, but of much greater extent and importance in Italy, on both 
sides of the Appenines. 
It would appear that what now bears the name of Italy, was at 
the time of its first emergence from the deep, but a long narrow 
ridge, consisting indeed merely of what is now the Appenines, 
with a sea of moderate depth on each side. On the flanks of 
10* 
