Ixvi PK0CEEDING3 OF THE GEOIOGICAL SOCIETY. 



this, even shoiild the two have been in consecutive and uninter- 

 rupted sequence in time. 



" The somewhat Cretaceous fades which exists, however, in the 

 Lower Landenian [of Belgium] and the Thanet-Sands fossils, is 

 to be recognized in some portion of the fauna of the London Clay 

 itself. Thus among the Echinodermata the Hemiaster, a common 

 Cretaceous genus, has three species in the London Clay, and but one 

 in the Barton Clay ; whilst the prevalence of Crinoids, amongst which 

 is a species of Bourgueticrinus, hitherto considered a Chalk-genus, and 

 three species of Pentacrinus, and the new Cainocrinus of Forbes, 

 are features more resembling those prevailing in Mesozoic than 

 those usual in Tertiary strata. The two genera of Asteridce (Astro- 

 pecten and Goniaster) which occur in the London Clay are common 

 in the Cretaceous strata, the Oolites, and Lias." 



" The London Tertiary group seems to have resulted in that order 

 of changes which, commencing with the elevation of a portion of the 

 Chalk area at the end of the Maestricht period, was followed by sub- 

 sequent depressions which led to the transgressive accumidation of 



the Lower Tertiaries from north to south I have before 



shown the probability of the existence of dry land to the south and 

 an open sea to the north during the Thanet-Sands period, and of 

 more insular conditions during the Woolwich and Beading series 

 period ; and now with respect to the London Clay the evidence tends 

 in the same direction." 



" To have just terms of comparison, we need a Cretaceous series 

 with a similar varied marine, sestuarine, and fluviatile fauna, such as 

 jlourished during the successive Tertiary periods. We have already 

 in the Maestricht beds a change in the fauna — a dying-out of many 

 old forms, and the appearance of many genera common in the Ter- 

 tiary series." 



" In considering all these singular vicissitudes, and in contem- 

 plating the extent to which certain more northern influences ope- 

 rated in giving to a large portion of the fauna of the London Terti- 

 aries an aspect much more closely resembling that of the present 

 day than is found to exist in many more recent deposits, the 

 question suggests itself of how far that law, enunciated by Prof. 

 E. Forbes, and according to which the distribution of Molluscs in 

 depths of southern seas is equivalent to their appearance at lesser 

 depths or at the surface in parallels of latitude of more northern 

 seas, may by analogy be applied geologically in accounting for any 

 abnormal condition in the vertical succession of organic remains 



