Professor Pictet on the Distribution of Fossils. 267 



than those which exist in our own days. This law has been 

 rather conjectured than demonstrated ; and it will readily be 

 understood that it cannot be definitively admitted till numer- 

 ous localities shall have been studied, and their fossils deter- 

 mined with sufficient accuracy. Observations which appear 

 worthy of credit tend to shew, that species common to Ame- 

 rica and Europe have been found in contemporary formations. 

 Others prove that the species which have inhabited the 

 fi^reater part of Europe during the periods preceding our own, 

 were distributed in the Asiatic continent and in the North- 

 ern regions more extensively than the existing species of 

 temperate Europe. If time confirm these facts, we may de- 

 duce from them some interesting consequences respecting 

 the state of the globe at different epochs. 



This wider dispersion of species may shew, as I have inti- 

 mated above, that the temperature of the earth has been 

 more uniform in ancient times than it is at present. If the 

 same species have been able to live throughout almost the 

 whole of America, while they cannot now do so, we may 

 thence infer that the climate of the extreme parts did not dif- 

 fer so much as in our day, from that of the regions situated 

 under the equator. Similar conclusions may be drawn from 

 the fact, that we find the same species in the middle of Eu- 

 rope and in the north of Russia. 



These facts, relating to the geographical distribution of 

 fossil species, may perhaps shew, by the comparison of marine 

 molluscs, that the seas have been less deep in ancient times 

 than in our own. The habitation of marine molluscs is 

 partly limited by the depth of the sea ; the majority of the 

 species cannot live in those places where the sun is too dis- 

 tant from the surface of the water. Their wider dispersion 

 in ancient times, may justify the belief that this cause did 

 not then exist. 



The foregoing laws seem to be established in a pretty sa- 

 tisfactory manner ; but that which we have yet to explain 

 appears of such a nature, that it ought not to be admitted 

 without great restrictions. 



Fifth Law. — The faunas of the most ancient formations 

 are composed of animals of a more imperfect organization, and 



