266 Professor Pictet oti the Distribution of Fossih. 



Moreover, some facts recently made known appear to fur- 

 nish contrary results, and to indicate that certain parts of 

 the globe have been subjected, at least for a very brief pe- 

 riod, to colder temperatures. Certain recent deposits have 

 been found in Sicily, consisting of shells whose analogues do 

 not now live in the Mediterranean Sea, although they exist 

 in the North Sea. In some similar localities in Scotland, 

 the fossils form a whole which can only be compared, in the 

 present day, to the fauna in Iceland and Greenland. These 

 facts are of the same nature as the preceding ; are entitled 

 nearly to the same confidence ; and if the former indicate a 

 more elevated degree of temperature, the latter give evi- 

 dence of a lower. 



It is likewise possible that new observations may modify 

 the expression of this law in other points of view. Some re- 

 cent investigations seem to prove that there has been, at cer- 

 tain epochs, less difference between the temperature of the 

 poles and the equator. I shall revert to this question when 

 explaining the fourth law. 



I am therefore of opinion, that the law I have just stated 

 cannot yet be established in a very precise manner ; and 

 that, in the actual state of the science, the facts merely prove 

 that there have been changes of temperature at different 

 epochs, and that the countries with whose fossils we are best 

 acquainted have sometimes had a warmer climate than at 

 present — and this is probably the most frequent case — and 

 at times, also, a colder climate. * 



Fourth Law. — The species which have lived in ancient 

 epochs have had a more extensive geographical distribution 



central heat must have exercised more influence than in our own days in 

 heating the atmosphere at the earth's surface. This idea, seductive at first 

 sight, is, perhaps, like many I shall have occasion to analyse, more specious 

 than real. The thickness of the cooled bed, at the eras when there was 

 vegetation and life on the surface of the earth, was probably always too 

 great to allow the interior heat exercising much influence. A rigorous 

 discussion of this question of terrestrial physics would probably furnish 

 results very much opposed to what has long been admitted. 



* For the causes of the changes of temperature on the surface of the 

 globe, see the treatises on Geology, and, in particular, the first volume 

 of Mr Lyell's Principles. 



