TRANSACTIONS OF SECTION C. 739 



even monotony of forms, and is very distinct from that of succeeding times. Still 

 the leading families of the Rhizocarpece, Equisetaceee, Lycopodiaceee, Wtlices, and 

 Conifers, established in Palaeozoic times, yet remain ; and the changes which have 

 occurred consist mainly in the degradation of the three first-named families, and 

 in the introduction of new type? of Gyrnnosperms and Phsenogams. These changes, 

 delayed and scarcely perceptible in the Permian and Early Mesozoic, seem to have 

 been greatly accelerated in the Later Mesozoic. 



6. On the Relative Ages of the American and the English Cretaceous and 

 Eocene Series. By J. Starkie Gardner, F.L.S., F.G.S. 1 



The paper is a contribution towards the determination of the ages of the 

 American Oretaceo-Eocene rocks, relative to those of Europe. 



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

 America. The lowest beds there are distinguished by the presence of well-developed 

 dicotyledonous leaves, associated with Ammonites and other Cretaceous mollusca, 

 considered to warrant their correlation with the Gault and Chalk of England. 

 Newer beds thought to be intermediate in age between Secondary and Tertiary are 

 distinguished by the incoming of palms and a new flora of Dicotyledons, associated 

 with Mosasaurus. The rest are correlated 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, aud from a Cretaceous to a Tertiary vertebrata. 

 The high development of the flora is, however, quite irreconcilable with the 

 accepted correlation. 



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

 that the subdivisions of the Cretaceous series were first determined for a limited area, 

 when different ideas of evolution and gradual passage prevailed, and subsequently 

 extended to embrace areas at a distance which may be, rightly or wrono-ly, 

 correlated with those of England 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 comprises only shore deposits, 

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

 deeper sea-deposit, comparable to the ' Blue mud' of the 'Challenger,' with a typi- 

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

 the equivalents of the Gault, deposited under differing physical conditiojis, correspond- 

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

 the shore or shallower water conditions preceding the Chalk. The Chalk itself ia 

 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 

 ' Globigerina Ooze.' The arguments against this view are refuted in detail, and the 

 suggestion made that the alleged shallower habitats in the tropics of the tew sur- 

 viving Mollusca may be due to the lower temperature prevailing now in the abyssal 

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

 they were able to live in the Chalk period. 



The whole Cretaceous series in the British area is the result of a gradual con- 

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

 Neocomian, became more serious with the Gault, and continued until the close 

 of the Chalk. The focus of the depression, so far as its results are accessible, was 

 the English 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 Gault, 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 



1 Printed in full in Geological Magazine, Dec. III., vol. i., pp. 4-92-506, 1884. 



3 b 2 



