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



contemporaneous in the geological sense, but synchronous 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 &quot; contemporaneous &quot; as employed by geolo 

 gists. 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 &quot; contemporaneous &quot; formations ; but when 

 ever any thoughtful geologist is asked whether he means to say 

 that they were deposited synchronously, he says, &quot;No, only 

 within the same great epoch.&quot; And if, in pursuing the inquiry, 

 he is asked what may be the approximate value in time of a 

 &quot;great epoch&quot; whether it means a hundred years, or a thousand, 

 or a million, or ten million years his reply is, &quot; I cannot tell.&quot; 



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 approximated sedimen 

 tary strata : while, for distant deposits, there seems to be no kind 

 of physical evidence attainable of a nature competent to decide 

 whether such deposits were formed simultaneously, or whether 

 they possess any given difference of antiquity. To return to an 

 example already given : All competent authorities will probably 

 assent to the proposition that physical geology does not enable 

 us in any way to reply to this question Were the British 

 Cretaceous rocks deposited at the same time as those of India, 



