206 ^ag Sermons, (gssags, aitb Jiurfwfos. [x. 



cession of living forms upon the surface of the globe ; 

 to tell us of a wholly different distribution of climatic 

 conditions in ancient times; to reveal the character 

 of the first of all living existences; and to trace out 

 the law of progress from them to us. 



It may not be unprofitable to bestow on these pro- 

 fessions a somewhat more critical examination than 

 they have hitherto received, in order to ascertain how 

 far they rest on an irrefragable basis ; or whether, after 

 all, it might not be well for palaeontologists to learn 

 a little more carefully that scientific " ars artium," the 

 art of saying "I don't know." And to this end let 

 us define somewhat more exactly the extent of these 

 pretensions of palaeontology. 



Every one is aware that Professor Bronn's "Unter- 

 suchungen" and Professor Pictet's "Traite de Paleon- 

 tologie" are works of standard authority, familiarly 

 consulted by every working palaeontologist. It is desir- 

 able to speak of these excellent books, and of their 

 distinguished authors, with the utmost respect, and in 

 a tone as far as possible removed from carping criticism ; 

 indeed, if they are specially cited in this place, it is 

 merely in justification of the assertion that the follow- 

 ing propositions, which may be found implicitly, or 

 explicitly, in the works in question, are regarded by 

 the mass of palaeontologists and geologists, not only 

 on the Continent but in this country, as expressing 

 some of the best-established results of palaeontology. 

 Thus : 



Animals and plants began their existence together, 

 not long after the commencement of the deposition of 

 the sedimentary rocks ; and then succeeded one another, 

 in such a manner, that totally distinct faunae and florae 

 occupied the whole surface of the earth, one after the 

 other, and during distinct epochs of time. 



