112 prof. a. c. seward : co^tribtjtion to [March 1 913, 



A glance at the table shows that, while there is a very close 

 similarity between the Wealden flora of England and the corre- 

 sponding floras in Eastern and "Western North America, the number 

 of cosmopolitan types is smaller than in the case of the Middle 

 Jurassic floras. This may be due in part to the smaller number 

 of records of Cretaceo-Jurassic plants, as compared with the richer 

 and more numerous collections from Middle Jurassic strata. The 

 contrast between Wealden and Middle Jurassic floras is com- 

 paratively small, and it is difficult to select species which in 

 themselves are safe criteria as to the occurrence of a "Wealden, as 

 distinct from a true Jurassic, flora. OnycJiiopsis mantelli, Weichselia 

 mantelli, and a few other types may be described as useful index- 

 plants pointing to a Wealden age ; but it is, as a rule, only by the 

 examination of a fairly large number of species that any definite 

 pronouncement is justifiable as to the value of palseobotanical data 

 in regard to age-determination. 



It must not be forgotten that there are several Wealden species 

 recorded from North- Western Germany, the Arctic regions, and 

 elsewhere, which have not as yet been discovered in the English 

 area. The Ginkgoales are a case in point: the genera Ginkgo and 

 Baiera, both fairly abundant in the Jurassic vegetation of East 

 Yorkshire, have not been found in the Wealden of England. The 

 fact that these plants existed in the Kimmeridgian Epoch in 

 Scotland, as also in the "Wealden flora of Germany, favours the 

 view that their absence from the list of English species (p. 107) 

 is one of the many lacunse which further search may be expected 

 to fill. 



IV. Bibliography. 



Bartholin, C. T. (92). ' Nogle i den bornholmske Juraformation forekommende 



Planteforsteninger ' Bot. Tidsskrift, Kjobenhavn, vol. xviii, p. 12. 

 Bartholin, C. T. (10). ' Planteforsteninger fra Holsterhus paa Bornholm ' 



Danmarks Geol. Undersog. ser. 2, no. 24. 

 Beret, E. W. (10). 'A Revision of the Fossil Plants of the Genera Acrosticho- 



pteris, Tceniopteris, Nilssonia, and Sapindopsis from the Potomac Group ' 



Proc. U.S. Nat. Mus. vol. xxxviii, p. 625. 

 Berry, E. W. (10 2 ). 'A Revision of the Fossil Plants of the Genus JS'ageiopsisof 



Fontaine ' Proc. U.S. Nat. Mus. vol. xxxviii, p. 185. 

 Berry, E. W. (11). 'A Lower Cretaceous Species of Schizseaceoe from Eastern 



North America' Ann. Bot. vol. xxv, p. 193. 

 Berry, E. W. (II 2 ). 'The Lower Cretaceous Deposits of Maryland' Maryland 



Geological Survey, Baltimore. (By W. B. Clark, A. B. Bibbins, & E. W. 



Berry.) 

 Berry, E. W. (II 3 ). 'Contributions to the Mesozoic Flora of the Atlantic Coastal 



Plain— VII ' Bull. Torrey Bot. Club, vol. xxxviii, p. 399. 

 Bommer, C. (10). ' Contribution a l'Etude du Genre Weichselia (Note preliminaire) ' 



Bull. Soc. Roy. Bot. Belg. vol. xlvii, p. 296. 

 Boodle, L. A. (95). 'Spores in a Specimen of Tempshya (Endogenites) ' Ann. 



Bot. vol. ix, p. 137. 

 Brongniart, Ad. (28). ' Histoire des Vegetaux Fossiles ' Paris, 1828-37. 

 Carruthers, W. (66). "' On some Fossil Coniferous Fruits ' Geol. Mag. vol. iii, 



p. 534. 

 Carruthers, W. (69). ' On some Undescribed Coniferous Fruits from the Secondary 



Rocks of Britain ' Geol. Mag. vol. vi, p. 1. 

 Carruthers, W. (70). ' On Fossil Cycadean Stems from the Secondary Rocks of 



Britain ' Trans. Linn. Soc. vol. xxvi, p. 675. 



