384 THE IMPERFECTION OF THE 



paratively rare occurrence of a stray individual being killed whilst 

 swimming a river or being mired in a bog ; but there are other cases 

 for which other explanations must be sought. 



II. Unrepresented Time : — In the second place, I have had occa- 

 sion to point out before that the geological record, or the series of the 

 stratified deposits, is itself very imperfect ; and this of necessity 

 causes vast gaps in our palseontological knowledge. In this connec- 

 tion I may briefly review the evidence which we possess as to the 

 immensity of the " unrepresented time " between some of our great 

 formations ; and I cannot do better than take the case of the 

 Cretaceous and Eocene Rocks, though any other would do as well. 

 In examining such a case, the evidence may be divided into two 

 heads, the one palseontological, the other purely physical, and each 

 may be considered separately. , 



The Chalk, as is well known, constitutes the highest member of 

 the Cretaceous formation, and is the highest deposit known in 

 Britain as appertaining to the great Secondary or Mesozoic Series. 

 It is directly overlaid in various places by strata of Eocene age, 

 which form the base of the great Tertiary or Kainozoic Series of 

 rocks. The question, then, before us is this — What evidence have 

 we as to the lapse of time represented merely by the dividing-line 

 between the highest beds of the Chalk and the lowest beds of the 

 Eocene % 



Taking the palseontological evidence first, it is found that out of 

 five hundred species of fossils known to occur in the Upper Creta- 

 ceous beds in England, only one Brachiopod and a few of the 

 Foraminifera have hitherto been detected in the immediately over- 

 lying Eocene beds. These, on the contrary, are replete with fossils 

 wholly distinct from the Cretaceous species. It may be said, there- 

 fore, that the entire and very extensive assemblage of animals which 

 lived in the later Cretaceous seas of Britain had passed away and 

 become extinct before a single grain of the Eocene Rocks had been 

 deposited. N'ow, it is, of course, open to us to believe that the 

 animals of the Chalk sea were suddenly extinguished by some 

 natural agencies unknown to us, and that the animals of the Eocenet 

 sea had been as suddenly and in as obscure a manner introduced 

 en masse into the same waters. This theory, however, calls upon the 

 stage forces of which we know nothing, and is contradicted by th& 

 whole tenor of the operations which we see going on around us at 



