x.] GEOLOGICAL CONTEMPORANEITY. 181 



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 life; without the 

 second, all the other statements cited, every one of which 

 implies a knowledge of the state of different 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 phaeno- 

 mena ; but, at the same time, it must be recollected that the 

 value of negative evidence depends entirely on the amount of 

 positive corroboration it receives. 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 &quot; haven t seen anybody their way ; &quot; 

 upon which the counsel for the other side immediately puts in 

 ten or twelve thousand feet of Devonian sandstones to make 

 oath they never saw a fish or a mollusk, 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 Cambrian rocks nowhere exhibit fossils, and hence no 

 living being could have existed in their epoch. 



To this there are two replies : the first, that the observational 

 basis of the assertion that the lowest rocks are nowhere fossili- 

 ferous is an amazingly small one, seeing how very small an area, 

 in comparison to that of the whole world, has yet been fully 

 searched; the second, that the argument is good for nothing 

 unless the unfossiliferous rocks in question were not only 



