TRANS ACTIONS OF SECTION C. 739 



even monotony of forms, ami is very distinct from that of succeedinsf time.". Still 

 the leading families of the Ithizocarpec/', Eqnisetacea;, Ljicupodiacea', Fi/ici.^; and 

 CoiiifcM', established in Palaeozoic times, yet remain ; and the chanj^es which liavo 

 (Uiurivd consist mainly in the depjradation of the tliree tirst-named familii's, and 

 ill till' introduction of new types of Gymnosperms and Phienonrains. These tlmnfres, 

 Joliived and scarcely ]iercc|)tihle in tlie Permian and I'-arly Mesozoic, seem to have 

 been jrrcatly aecolerated in (ha Later Mesozoic. 



G. Oil the llelatice yl^o" of the Americmi and the EiKjUsh Cretaceous and 

 Eocene Series. Ihj J. Staijkib Gakdneu, F.L.S., F.G.S.^ 



Thi^ paper is a contrihution towards the determination of the a<jes of the 

 American Cretaceo-Eoceno I'ncks, relative to those of luirope. 



It briefly describes tlie chief characteristics of the various stages of the series in 

 America. The lowest beds there are distinguished'oy the presenceof well-developed 

 dicotyledonous leaves, associated with Aimno/iitrs and other Cretaceous mollusca, 

 considered to warrant their correlation with the Gault and ("halk of England, 

 Xewer beds thought to bo intermediate in ag(; between Secondary and 'J'ertiaiy arc 

 (listuiguished by the incoming of palms and a new flora of Dicotylt^dons, associated 

 with M'isasaiin'.i. The rest are correlatt.Ml with the various divisions of the Tertiary 

 series recognised in Europe. The entire series seems to have been deposited with- 

 out any considerable break in continuity, but reveals a sudden transition from a 

 temperate to a subtropical flora, and from a Cretaceous to a Tertiary vertebrata. 

 Tlie Idgh development of the llora is, however, quite irreconcilable with the 

 accepted correlation. 



In further comparing the American series with that of Europe, it is oliserved 

 that the subdivisions of the Cretaceous series were tirst determhied for a limited area 

 wlitii ditl'erent ideas of evolution and gradual passage prevailed, and subsequently 

 extended to embrace areas at a distance which may be, rightly or wrongly, 

 correlated with those of ICngland and western France. The comparisons now 

 drawn are only between the rocks of the original and typical area and of America, 

 excluding the Cretaceous rocks of other countries. 



Thus restricted, the Neocomian of Europe comjn'ises only shore deposits, 

 characterised by a Cretaceo-.Turassic fauna and a .Jurassic flora. The Cault is a 

 deeper sea-deposit, comparable to the ' Blue mud' of the '( "liallenger,' with a typi- 

 cally Cretaceous fauna and a .Jurassic flora. The Upper Greensands are more or less 

 the efpuvalentsoftheCiault, deposited under differing physical conditions, correspond- 

 ing to the ' Greensands' of the * Challenger,' and have been assumed to represent 

 tlic shore or shallower water conditions preceding the Chalk. The Chalk itself is 

 described with a view to prove that it is a truly oceanic deposit, formed at a distance 

 from shore and at a considerable depth, corresponding in all respects with the existing 

 ' Glo})igerina Ooze.' The arguments against this view are refuted in detail, and the 

 suggest ion made tliat the alleged shallower habitats in the tropics of tlie few sur- 

 viving Mollusca maj- be due to the lower ttnnperature prevailing Jiow in the abyssal 

 deptiis of the ocean having driven heat-loving types from the depths at which 

 t!iey were able to live in the Chalk period. 



The whole Cretaceous series in the British area is the result of a gi'adual con- 

 version of land into sea, owing to subsidence. The process commenced with the 

 Neocomian, became more serious with the (fault, and continued until the close 

 of the (j'halk. The focus of the depression, so far as its results arc accessible, was 

 the p]nglisli Channel, whence it spread in an easterly direction across Central 

 Europe. As the land subsided, the gulf increased in magnitude, and Blue and 

 Green Muds were formed on a wider and wider area, to be succeeded in due time 

 by chalky Ooze. The nearer the focus of subsidence, the older the Greensands 

 and Gauit, and the farther we recede from it, the newer in age they become. The 

 zones of increasing depth travelled outward and forward, and though now re- 

 presented by continuous bands of the same lithological characters, extending over 



' Printed in full in Geological Magazine, Dec. III., vol, i., pp. 492-.''.06, 1884. 



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