70 INTRODUCTION. 



Europe generally there are but fragmentary traces of such. We 

 may be quite sure, however, 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. 



It is not probable that we shall ever discover any very consider- 

 able portion of these, considering the large extent of the terrestrial 

 surface which is covered by the ocean. In New Zealand, however, 



Fig. 15. — Section showing strata of Tertiary age (a), resting upon a worn and denuded surface 

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



and still more notably in North America, extensive deposits are 

 already known, which were laid down subsequent to the formation 

 of the White Chalk and prior to the deposition of the Eocene Ter- 

 tiary, and which serve, therefore, to partially bridge over the great 

 hiatus which separates these formations in Europe. These tran- 

 sitional formations are charged, as might have been anticipated, 

 with the remains of animals which in part resemble Cretaceous 

 types and in part are characteristic Eocene forms. 



The break between the Cretaceous and lowest Tertiary de- 

 posits is one of the most extensive and universal of which we have 

 at present any knowledge. Almost equally extensive and wide- 

 spread is the break which separates the Palaeozoic from the Meso- 

 zoic group of deposits. Throughout the whole stratified series, 

 however, we meet at intervals with physical and palaeontological 

 breaks of greater or less magnitude. Sometimes a palaeontological 

 break occurs unaccompanied by marked physical disturbance or 

 discordance of the strata ; but usually a gap in the succession of 

 life-forms is associated with clear physical evidence of elevation and 

 subsequent denudation. 



It may be pointed out that the unconformities above alluded to 

 must be distinguished from the common cases in which strata of 

 one age are locally superimposed in an unconformable manner upon 



