50 GEOLOGICAL SURVEY 
into three parts. The upper includes the Maestricht beds, and the chalk; to the middle belong the 
Upper greensand and Gault ; and in the lower is placed the Lower greensand. 
In Switzerland the lower division is represented by the Neocomien formation, which is found 
near Neufchatel. 
In the United States the Cretaceous group is well represented along the coast of the Atlantic 
States, beginning at New Jersey. It is found in North Carolina, and it is exposed on the banks of 
the rivers in the Eastern part of South Carolina. 
My. Lyell, who had examined these beds nearly throughout their entire extent, refers them to 
that part of the formation included between the Maestricht beds and the Gault inclusive. In this 
country the formation is every where characterised by Belemnites Americana, Exogyra Costata, 
Gryphza Mutabilis, and two or three species of Ammonites. In Alabama a very large species of 
Hippurites occurs, which is often a foot in diameter. 
The most remarkable reptile is the Mososaurus, a genus common to this continent and that of 
Europe. : 
The Ammonitide, after existing here in vast numbers, disappear forever. It is remarkable that 
the beds of chalk that every where characterize this formation in Europe should be entirely absent 
in America. In some of the New Jersey beds calcareous matter is abundant, but in North and 
South Carolina it forms not more than 25 or 30 per cent. of the mass, and in Alabama the forma- 
tion becomes again highly calcareous. 
Tertiary Preriop. 
The Tertiary rocks are every where very variable in mineral composition and state of aggrega- 
tion. Loose sands, gravel, clay, limestones and marl, are the principal materials which make up 
these rocks. Although widely distributed, they are not often found in continuous strata, but filling 
depressions in the underlying rocks. For a long time much confusion existed in relation to the 
relative age of the numerous formations comprised in the Tertiary period. The opening of the 
beds of the Paris hasin, and the investigation by Brogniart and Cuvier of the organic remains 
brought to light, directed attention to this interesting field of enquiry. ‘Tertiary fossils were 
collected, studied with care, and compared with living types; it soon became evident that many of 
the fossils were identical with living species. Of 1122 species of fossil shells, found in the Paris 
basin, 38 were identified with living forms by M. Deshayes, who first suggested that the Tertiary 
formations may be divided according to the relative proportion of extinct and living fossil shells 
which they may contain. 
But it is to Mr. Lyell that we are indebted for a classification founded on this principle. At the 
time that this classification was proposed there were known from the Paris basin and other con- 
temporaneous beds 1234 shells, of which 42, or about three and a half per cent. were living species. 
To such beds Mr. Lyell has given the name “Eocene,” which implies the dawn of the present 
state of things on the earth; for it is here that we find the first species that has a living representa- 
tive ; besides, the whole group resembles those now inhabiting our seas. 
In other deposits Mr. Lyell found that the proportion of living to extinct species amounted to 
