FOSSILS. 



progressive increase in the number or proportion of recent species 

 found : in the Paris basin three per cent, of the fossil shells are 

 analogous to the shells now existing ; in the miocene, eighteen per 

 cent., and in the pliocene fifty per cent, of the fossil shells resem- 

 ble existing species. There is scarcely any analogy between the 

 shells of the Paris basin limestone and those of the subapennine 

 hills. Besides the Balanus crasus (fig. 1(51), and the Rostella!- 

 ria pespeliea'ni (Jig. 162), we may cite the Pleuro'toma rota' fa 

 (fig. 172), the Buc'cinum prisma'ticum (Jig. 173), the Volu'ta 

 Lambe'rti (Jig. 174), &c., and almost all the shells of the Mediter- 

 ranean. 



Fig. HZ.Pleuro'loma 

 rola'ta 



Fig. 173. Buc'cinum 

 prisma'ticum. 



Fig. 174 Volu'ta 

 Lambe'rti. 



Fig. 175 Murex 

 alveola'tus. 



Fig. 



176. Astarte Bag. 

 teroii. 



Fig. lll.Cy'prea 

 coccinello'ides. 



The deposits alluded to also contain masses of lignites, which arc advan- 

 tageously worked in different localities. Some offer regular layers of a sort 

 jf compact coal (brown coal), accompanied by fresh-water shells, indicating 

 a tranquil deposit in lakes; but the greatest number contain only irregular 

 masses of wood, some of which present the texture of the con'ifers. A 

 great number of leaves, analogous to those of existing dicoty'ledons, are 

 also found. 



27. What proportion of fossils found in the eocene, miocene, and plio- 

 cene respectively, resemble species now living ? 



