Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/84

 this, even should the two have been in consecutive and uninterrupted 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 Asteridoe (Astropecten 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 subsequent depressions which led to the transgressive accumulation 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, aestuarine, and fluviatile fauna, such as nourished 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 Tertiary series."

" In considering all these singular vicissitudes, and in contemplating the extent to which certain more northern influences operated in giving to a large portion of the fauna of the London Tertiaries 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