Geological Society. 247 



' Pourquoi Pas,' 1913, p. 129, fig. 81), it does not show the 

 enlargement of the dorsal processes of the trunk-somites 

 which seems to be characteristic of full-grown specimens of 

 the last-named species. 



PROCEEDINGS OF LEARNED SOCIETIES. 



GEOLOGICAL SOCIETY. 



March 24th, 1920.— Mr. R. D. Oldham, F.R.S., 

 President, in the Chair. 



The following communications were read : — 



1. ' On Two Preglacial Floras from Castle Eden (County 

 Durham).' By Mrs. Eleanor M. Reid, B.Sc, F.L.S., F.G.S. 



The seeds examined were obtained by Dr. C. T. Trechmann from 

 Preglacial clays, found in fissures of the Magnesian Limestone at 

 Castle Eden. The clays were carried by the Scandinavian ice from 

 the area now covered by the North Sea. 



The study proved the presence of two seed-bearing clays, of 

 different ages," the earlier being undoubtedly Pliocene. The 

 Pliocene age is confirmed by M. P. Lesne, who determined the 

 insect-remains found intermingled with the seeds. 



"While the work was in progress, material from the base of the 

 Pliocene of Pont de Gail (Cantal) gave knowledge, for the first 

 time, of a seed flora of known age, low down in the Pliocene ; it 

 showed that the rate of change in the character of the West 

 European Pliocene flora was slower than had been suggested by 

 Clement Reid and the Author. 



A critical comparison was made between the Cromerian, Teglian, 

 Castle-Eden, Reuverian, and Pont-de-Gail floras, on the bases of 

 the percentages of all exotics, and of Chinese-North American 

 exotics (that is : plants now inhabiting the Far East of Asia or 

 North America, but not Western Europe), in each flora. The 

 result proved the Reuverian to be Lower Pliocene, not top of the 

 Middle Pliocene (as formerly suggested) ; and the Castle-Eden flora 

 to he Middle Pliocene. 



Therefore a study of fossil seeds had made it possible to dis- 

 criminate between strata intimately mixed in situ, and to determine 

 their geological age when unknown. 



