iLNOTTERSART ADDRESS. xliil 



faunse and florae occupied the whole surface of the earth, one after 

 the other, and diu-ing distinct epochs of time. 



A geological formation is the sum of all the strata deposited over 

 the whole siu'face of the earth during one of these epochs : a geo- 

 logical 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 distribution of living beings 

 in zones is the result of a gmdual lowering of the general tempe- 

 rature, which fii'st 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 ftmdamental assumptions upon which they all logically de- 

 pend ? and what is the evidence on which those fundamental proposi- 

 tions demand our assent ? 



These assumptions are two : the first, that the commencement of 

 the geological record is coeval with the commencement of life on the 

 globe ; the second, that geological contemporaneity is the same thing 

 as chronological synchrony. Without the first of these assumptions 

 there would of course be no ground for any statement respecting the 

 commencement of hfe ; without the second, all the other statements 

 cited, every one of which implies a knowledge of the state of dif- 

 ferent parts of the earth at one and the same time, will be no less 

 devoid of demonstration. 



The first assumption obviously rests entirely on negative evidence. 

 This is, of course, the only evidence that ever can be available to 

 prove the commencement of any series of phenomena ; but, at the 

 same time, it must be recollected that the value of negative evidence 

 depends entirely on the amount of positive corroboration it re- 

 ceives. If A B wishes to prove an alibi, it is of no use for him to 

 get a thousand witnesses simply to swear that they did not see him 

 in such and such a place, unless the witnesses are prepared to 

 prove that they must have seen him had he been there. But the 

 evidence that animal life commenced with the Lingula-flags, e. g., 

 would seem to be exactly of this unsatisfactory uncorroborated sort. 

 The Cambrian witnesses simply swear they " haven't seen anybody 

 their way ; " upon which the counsel for the other side immediatery 

 puts in ten or twelve thousand feet of Devonian sandstones to make 

 oath they never saw a fish or a moUusk, though all the world knows 

 there were plenty in their time. 



But then it is urged that, though the Devonian rocks in one part 

 of the world exhibit no fossils, in another they do, while the lower 



