378 GEOLOGICAL CONTEMPORANEITY 



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 professions 

 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 paleontologists to learn a little more care- 

 fully 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 paleontology. 



Every one is aware that Professor Bronn's Untersuchungen 

 and Professor Pictet's Traili de Paleontologie are works of 

 standard authority, familiarly consulted by every working 

 paleontologist. It is desirable 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 following propositions, which may be found implicitly, 

 or explicitly, in the works in question, are regarded by 

 the mass of paleontologists and geologists, not only on the 

 Continent but in this country, as expressing some of the 

 best-established results of paleontology. Thus : 



Animals and plants began their existence together, not 

 long after the commencement of the deposition of the sedi- 

 mentary 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. 



A geological formation is the sum of all the strata 

 deposited over the whole surface of the earth during one 

 of these epochs : a geological fauna or flora is the sum 

 of all the species of animals or plants which occupied the 

 whole surface of the globe, during one of these epochs. 



The population of the earth's surface was at first very 

 similar in all parts, and only from the middle of the Tertiary 

 epoch onwards, began to show a distinct distribution in 

 zones. 



The constitution of the original population, as well as 

 the numerical proportions of its members, indicates a 

 warmer and, on the whole, somewhat tropical climate, 

 which remained tolerably equable throughout the year. 



