ANNIVERSARY ADDRESS TO THE GEOLOGICAL SOCIETY 517 
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 assump- 
tion. 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 when- 
ever 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 authori- 
ties 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 sedimentary 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 differ- 
ence or 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, or are they a million of years younger or a 
million of years older ? 
Is paleontology able to succeed where physical geology fails? 
Standard writers on paleontology, as has been seen, assume that she 
can. They take it for granted, that deposits containing similar organic 
remains are synchronous—at any rate in a broad sense; and yet, 
those who will study the eleventh and twelfth chapters of Sir Henry 
De la Beche’s remarkable “ Researches in Theoretical Geology,” pub- 
lished now nearly thirty years ago, and will carry out the arguments 
