IX GEOLOGICAL CONTEMPORANEITY 281 



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 

 " contemporaneous " formations ; but whenever 

 any thoughtful geologist is asked whether he 

 means to say that they were deposited synchron- 

 ously, 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 



