G2 INTRODUCTION. 



necessity causes vast gaps in our palseontological knowledge. 

 In this connection we may briefly consider the evidence which 

 we possess as to the immensity of the " unrepresented time " 

 between some of the great formations, and no better example 

 can be chosen than that of the Cretaceous and Eocene rocks, 

 as developed in Europe. In considering such a case, the 

 evidence may be divided into two heads, the one palaeonto- 

 logical, the other purely physical, and each may be looked 

 at separately. 



The Chalk, as is well known, constitutes in Britain the 

 highest member of the Cretaceous formation, and is the 

 highest deposit there known 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 in the Upper 

 Cretaceous beds, only one Brachiopod and a few Foraminifera 

 have hitherto been detected in the immediately overlying 

 Eocene beds. These latter, on the contrary, are replete with 

 organic remains wholly distinct from those of the Cretaceous 

 beds. It may be said, therefore, that the very, extensive as- 

 semblage of animals which lived in the later Cretaceous seas 

 of Britain had entirely passed away and become a thing of 

 the past, before a single grain of the Eocene rocks had been 

 deposited. Now 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 Eocene sea had been in as sudden and 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 the whole tenor of the 

 operations which we see going on around us at the present 

 day. It is preferable, therefore, to believe that no such 

 violent processes of destruction and re-peopling took place, 



