of the Northern Regions. 149 



nothing short of some general change in the })hysical condition 

 of the earth's surface can account for such a discrepance in the 

 ancient and actual races of its inhabitants ; and as we find that 

 temperature limits the species which still exist, the analogy is 

 surely favourable to the supposition that a change of tempera- 

 ture has been the cause of this difference. 



5. The CrocodUidcr. — This family actually includes many 

 species, and is exclusively limited to warm latitudes. I have 

 been enabled to ascertain ten distinct fossil species, six occurring 

 in this island. They are all of the division Leptorrhyncus. One 

 of these in the tertiary strata approaches very nearly to the ex- 

 isting species. Of these I hope shortly to lay a detailed account 

 before the Geological Society. 



I will pause here to consider for a moment the nature of the 

 resulting argument. If the actual limitation can be predicated 

 only of species, and not of genera, how comes it that not one of 

 the many species included has wandered into colder regions .'' 

 I here find a genus having numerous fossil and numerous recent 

 species ; and I know all the recent species to be confined within 

 warm latitudes. Does not every law of analogy warrant me 

 in considering it at least probable that the fossil species were 

 similary confined ? I find that these animals must once have 

 swarmed in localities where they are now extinct. It is impossi- 

 ble to contemplate so extraordinary a fact, without being led to 

 the inquiry, whether any probable cause can be assigned for it ; 

 and analogy again presents a diminution of temperature as a 

 sufficient cause, seeing that the genus is now limited by tem- 

 perature. Has Dr Fleming any more probable solution of the 

 problem to offer ? or can he prove that this is in itself so im- 

 probable that the presumptions in its favour cannot be ascer- 

 tained ? 



The other fossil Saurians may be objected to, as too remote 

 from any existing types to admit lany argument from analogy ; 

 but without pressing the subject, I will observe that all the 

 larger living tribes are confined to warm latitudes. 



6. Testudinata. — The existing Chelonians, with a few minute 

 exceptions, are also confined to warm latitudes, in the actual 

 order of things; yet their occurrence in a fossil state is very 

 common in our strata, especially in the limestone of Purbeck, 



