34 



INTRODUCTION. 



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. 3). 



Fig. 3. Section showing strata of Tertiary age (a), resting upon a worn and denuded 

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



In the unconformability, 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 frag- 

 mentary traces of such. We may be quite sure, however, that 

 during the time represented in Britain by the mere line of un- 

 conformability between the Chalk and the Eocene, there were 

 somewhere deposited considerable accumulations of sediment. 

 Whether we shall ever succeed in discovering these, or any 

 part of these, is, of course, uncertain. We may be certain, 

 however, that such deposits, if ever discovered, will prove to 

 be charged with the remains of animals more or less inter- 

 mediate 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. 



Amongst other well-known instances of more or less general 

 unconformity in the stratified series, may be mentioned that 

 between the Lower and Upper Silurian (not always present), 

 that between the Lower and Upper Old Red Sandstone (also 

 not universal), that between the Carboniferous and Permian 

 Rocks, that between the Permian and Triassic Rocks (not 

 universal), and that between the Lower and Upper Cretaceous 



