170 THEORY OF THE EARTH. 



conceived to be of very modern origin, has been 

 shown in that extensive examination to have ori- 

 ginated at a period considerably far back in the 

 age before the last; or, in other words, to have 

 owed its origin to causes connected with the revo- 

 lution and catastrophe before the last general 

 irruption of the waters over our present habitable 

 world. 



It would now be of great importance to examine 

 the other basins containing chalk formations, and 

 in general to pay particular attention to the strata 

 which rest upon that formation, that these may be 

 compared with those we found in the environs of 

 Paris. Perhaps the chalk itself may be found to 

 contain some successive depositions of organic re- 

 mains. It is surrounded and supported by the 

 compact limestone, which occupies a great pro- 

 portion of France and Germany, and the extra- 

 neous fossils of which are extremely different from 

 all those of our basin. But, in following the com- 

 pact limestone, from the chalk to the limestone 

 of the central ridges of Jura, which are almost 

 devoid of shells, or to the aggregated rocks of the 

 acclivities oftheHartz, the Vosges, and the Black 

 Forest, we shall probably find abundance of varia- 

 tions: And the gryphites, the cornua ammonis, 

 and the entrochi, with which it abounds, may per- 

 haps be found distributed by genera, or at least 

 by species. 



