Address delivered at the anniversary meeting of the Geological Society of London, on the 17th of February, 1871 : prefaced by the announcement of the award of the Wollaston Medal and proceeds of the donation-fund for the same year / by Joseph Prestwich.
- Joseph Prestwich
- Date:
- 1871
Licence: Public Domain Mark
Credit: Address delivered at the anniversary meeting of the Geological Society of London, on the 17th of February, 1871 : prefaced by the announcement of the award of the Wollaston Medal and proceeds of the donation-fund for the same year / by Joseph Prestwich. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![this, even should the two have been in consecutive and uninter- rupted sequence in time. “ The somewhat Cretaceous facies 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 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, [estuarine, and fluviatile fauna, such as flourished 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 tho surface in parallels of latitude of more northern seas, may by analogy bo applied geologically in accounting for any abnormal condition in the vertical succession of organic remains](https://iiif.wellcomecollection.org/image/b22446102_0046.jp2/full/800%2C/0/default.jpg)
