108 HISTORY OP THE EARTH. 
the secondary formations is the chalk that presents itself so 
conspicuously in the cliffs of Dover to a person who is approach- 
ing the island from the southeast. It abounds in organic remains, 
but until recently was supposed not to contain a single species 
that is known to inhabit the earth at the present time. Since the 
deposition of the chalk therefore, it appeared that the population 
of the earth had undergone a total change, not only in regard to 
the individuals occupying it but in regard to species. 
Above the chalk, in Messrs. Conybeare and Philips' Outlines 
of the Geology of the country, there are noticed and described 
three or four formations in the neighbourhood of London, and 
upon, and near the Isle of Wight, of limited extent, where the 
species now inhabiting the ocean begin to make their appearance ; 
at first or in the lower beds ; rarely, and mixed with a large num- 
ber of extinct species, but afterwards in greater variety. Here 
then the line of demarcation was drawn between the seconda- 
ry and tertiary strata, the former, being such as contain extinct 
species only , the latter, an intermixture in larger or smaller num- 
bers, of species that are recent or still living. 
Very recently, Ehrenberg, employing the microscope in these 
investigations, has ascertained that a great number of shells, most- 
ly too small to be accurately distinguished by the naked eye, are 
common to the chalk and the more recent strata. But the line 
of separation here indicated, will probably not be changed on that 
account. 
It was formerly held that the deposition of the chalk, the new- 
est of the secondary strata, was an event of comparatively recent 
occurrence, and if not actually within it, approaching the borders 
of our own time. This opinion is now abandoned, and the chalk 
referred to an era exceedingly remote ; separated in fact from the 
present day, by ages, compared with which the period embraced 
by human records whether sacred or profane, is but a brief and 
evanescent term of duration. We have now to state the facts and 
observations on which these new views and doctrines are founded. 
The tertiary district that first attracted particular notice is that 
which surrounds the city of Paris, embracing an area of about 
7100 square miles, equal to the one seventh part of the state of 
North Carolina. It is commonly called the Paris basin, that city 
being nearly in its centre. It is surrounded by chalk on every 
side except the south, and southwest, in which directions that form- 
ation is wanting, and the tertiary beds rest upon the strata under- 
lying the chalk. 
When a new impulse was given to the study of Geology at 
Freyburg, the attention of Werner and his disciples was directed 
principally, and with the most interest, to the more ancient rocks. 
To these succeeded as objects of study and investigation, the se- 
condary strata, especially those of England. It was not till the 
publication of the " Mineralogical Geography of the Environs of 
the city of Paris," by Cuvier and Brongniart, in 1811, that the 
