64 INTRODUCTION. 



wholly indefinite period, the Chalk was again submerged 

 beneath the sea, in which process it would be subjected to 

 still further denudation, and an approximately level surface 

 would be formed upon it. Fourthly, strata of Eocene age 

 were deposited upon the denuded surface of the Chalk, 

 filling up all the hollows and inequalities of its eroded sur- 

 face (fig. 10). 



Fig. 10. Section showing strata of Tertiary age a , resting upon a worn and denuded 

 surface of White Chalk (Z>), the stratification of which is marked by lines of flints. 



Iii the unconforrnability, then, between the Chalk and the 

 Eocene rocks, we have unequivocal evidence irrespective 

 of anything that we learn from Palaeontology that the break 

 between the two formations was one of enormous length. In 

 Britain the interval of time thus indicated is not represented 

 by any deposits ; and in Europe generally there are but 

 fragmentary traces of such. We may be quite sure, how- 

 ever, that during the time represented in Britain by the 

 mere line of unconformability between the Chalk and the 

 Eocene, there were somewhere deposited considerable accu- 

 mulations of sediment. Whether we shall ever succeed in 

 discovering these, or any part of these, is, of course, uncer- 

 tain. We may be certain, however, that such deposits, if 

 ever discovered, will prove to be charged with the remains 

 of animals more or less intermediate in character between 

 those of the Cretaceous and those of the Eocene period ; and 

 the huge gap now existing between these formations will 

 thus be more or less completely bridged over. Indeed, in 

 North America we actually find such a series of deposits, 



