THE PRE-ADAMITE EARTH. 



parts submerged becoming dry land. During each period the 

 deposition of strata corresponding to it, has been of course con- 

 fined to such parts of the earth only as were covered by water, 

 and hence we are able to trace the geographical limits of sea and 

 land, by tracing the limits of the deposits characteristic of each 

 stratum. 



Thus, during the Silurian period, the Silurian strata have been 

 deposited only on those parts of the globe which were during that 

 period covered by water, but not on those which formed the 

 land. When we use the expression, therefore, the Silurian sea, 

 we must be understood to mean that portion of the globe which, 

 during the Silurian period, was covered by water, and those 

 portions must necessarily be co-extensive with and limited by 

 Silurian deposits. In the same manner during the Cretaceous 

 period, the globe, as before, consisting of land and water, the 

 cretaceous deposit was made only in those parts which were then 

 covered by water, and formed the bottom of what is called the 

 Cretaceous sea ; the other parts of the earth, which at that epoch 

 formed the land, being consequently destitute of the cretaceous 

 strata. 



In the same sense is to be understood the expressions, the Tri- 

 assic sea, Jurassic sea, Tertiary sea, and so on. 



The absence, therefore, of any particular deposit in an extent 

 more or less considerable of the crust of the earth, indicates that 

 the subjacent deposit was above the level of the sea, and formed 

 an island or continent more or less elevated during the period in 

 which the absent deposit was made. Thus, for example, an 

 extensive plateau in the centre of France must have been dry 

 land from the most remote geological epochs ; and at the epoch 

 of the formation of the deposit which constitutes the present Paris 

 basin, the greatest part of Europe must have been dry land, 

 while Paris and a large tract surrounding it, as well as Bordeaux 

 and the surrounding regions, were covered by the sea, as will be 

 more fully explained hereafter. 



But it happens also that the parts which thus prove to have 

 been dry land at a certain geological epoch, have been afterwards 

 covered by more modern sediments ; from whence it follows that 

 they must have subsequently sunk beneath the ocean, so as to 

 receive these new deposits. It is by such subsidences of the land 

 that some of the geological convulsions, whose traces will be 

 hereafter noticed, have been explained. 



200. According to the results obtained from the researches of 

 M. Elie de Beaumont, it appears from a comparison of the various 

 mountain ranges of Europe, and from an examination of the 

 strata upon their slopes and at their bases, that since the solidifi- 



