180 LAY SERMONS, ESSAYS, AND REVIEWS. [x. 



tone as far as possible removed from carping criticism ; indeed, 

 if they are specially cited in this place, it is merely in justifi 

 cation 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 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, 



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. The subsequent dis 

 tribution of living beings in zones is the result of a gradual 

 lowering of the general temperature, which first began to be felt 

 at the poles. 



It is not now proposed to inquire whether these doctrines are 

 true or false ; but to direct your attention to a much simpler 

 though very essential preliminary question What is their 

 logical basis ? what are the fundamental assumptions upon 

 which they all logically depend ? and what is the evidence on 

 which those fundamental propositions demand our assent ? 



These assumptions are two : the first, that the commencement 



