AKNIVEKSAET ADDKESS OF THE PRESIDENT. Ixv 



the States, wiiich is bordered by Tertiary strata of a like character 

 with their European equivalents. 



It is true there have been elevations of the Cretaceous and 

 Tertiary strata during the Tertiary period far greater than the 

 depths first mentioned ; but it has been in mountain-chains which 

 have little affected the great plains of continental land. In the 

 same way there may have been partial elevations in the bed of 

 the Postcretaceous Atlantic ; but there is nothing to indicate that 

 it has ever been entirely raised. I think, therefore, that the hypo- 

 thesis with regard to the continuity of that sea-bed from the period 

 of the Chalk to the present period is one of high probability. 



If such a northern land barrier as that which I have alluded to 

 existed at the period of the Chalk, and that barrier was submerged 

 during the early part of the Tertiary period, it would (taken in con- 

 junction with the very different conditions of depth under which 

 the Chalk and Lower Tertiaries were formed) go far to account for 

 the great break in the fauna of the two periods. Some years since 

 I had occasion to show on other grounds that the Thanet Sands, 

 which repose on the Chalk in the south-east of England, exhibited 

 a fauna essentially of temperate or cold latitudes, and I inferred 

 the inset of currents from the north. As those remarks bear upon 

 the present question, I will quote some of the passages in the paper 

 to which I refer *. 



" In viewing the London Tertiaries as a group, and comparing 

 them directly with the underlying Chalk, it is to be observed that 

 we are not comparing like terms of the two periods. That a great 

 and essential difference existed between these periods must be ad- 

 mitted ; but it is a question how far that difference is widened by 

 the comparison being instituted between the deep and shallow sea 

 deposits, instead of between strata deposited under like conditions 



during those two periods The adaptation of this area at the 



Thanet-Sands period to the existence of the numerous shallow- 

 water burrowing LameUibranchiates, whatever the duration of the 

 intervening time, would necessarily unfit it for the deeper-sea 

 Cephalopoda, Brachiopoda, and other famihes which prevail in our 

 Cretaceous series. 



" We have therefore, in viewing the Tertiary strata in relation 

 to the underlying Chalk, to take into consideration that the exist- 

 ence of certain classes of fossils in the former of necessity implies 

 the non-existence of other classes found in the latter deposit — and 

 * Quart. Journ. Geol. Soc. vol. x. p. 443, Nov. 1854. 



