x. I (^ologiral (&vnhm$Qxmu%i$. 209 



in the chronological sense. To use the alibi illustration 

 again. If a man wishes to prove he was in neither 

 of two places, A and B, on a given day, his witnesses 

 for each place must be prepared to answer for the 

 whole day. If they can only prove that he was not 

 at A in the morning, and not at B in the afternoon, 

 the evidence of his absence from both is nil, because 

 he might have been at B in the morning and at A in 

 the afternoon. 



Thus everything depends upon the validity of the 

 second assumption. And we must proceed to inquire 

 what is the real meaning of the word "contemporaneous" 

 as employed by geologists. To this end a concrete 

 example may be taken. 



The Lias of England and the Lias of Germany, the 

 Cretaceous rocks of Britain and the Cretaceous rocks 

 of Southern India, are termed by geologists "contem- 

 poraneous" formations; but whenever any thoughtful 

 geologist is asked whether he means to say that they 

 were deposited synchronously, he says, "No, only 

 within the same great epoch/' And if, in pursuing 

 the inquiry, he is asked what may be the approximate 

 value in time of a " great epoch " whether it means 

 a hundred years, or a thousand, or a million, or ten 

 million years his reply is, "I cannot tell." 



If the further question be put, whether physical 

 geology is in possession of any method by which the 

 actual synchrony (or the reverse) of any two distant 

 deposits can be ascertained, no such method can be 

 heard of; it being admitted by all the best authorities 

 that neither similarity of mineral composition, nor of 

 physical character, nor even direct continuity of stratum, 

 are absolute proofs of the synchronism of even approxi- 

 mated sedimentary strata : while, for distant deposits, 

 there seems to be no kind of physical evidence attain* 



P 



