148 MKS. E. M. EEID : A COMPARATIVE [vol. lxxvi, 



received two more Pliocene seed-collections for study. The one, 

 derived from material ploughed by the advancing Scandinavian 

 ice-sheet from some part of the area now covered by the North 

 Sea, and thrust as a glacial erratic into fissures of the Magnesian 

 Limestone at Castle Eden, on the Durham coast ; and the other 

 from Pont-de-Gail in Cantal. 1 



The Pont-de-Gail deposit has proved of the utmost importance 

 in the study of Pliocene seeds, for its age is known. MM. G. F. 

 Dollfus and P. Marty state, from a study of the mollusca, that it 

 lies at the base of the Pliocene. 2 For the first time this deposit 

 has given knowledge of a seed flora of definite age, low down in 

 the Pliocene. 



As at present known, it is a small flora, consisting of but 

 48 species ; but, while Avorking at it, I was continually impressed by 

 its resemblance to the Reuverian flora. There was the same large 

 proportion of extinct and exotic species, of species belonging to 

 the Chinese-North American association, and of mountain-plants ; 

 .and, of the forty-eight species, three were Reuverian. So striking 

 was the relationship that I felt certain that the two floras must be 

 very nearly of the same age, and was led to try to compare them. 



It was difficult to decide, where determinations were necessarily 

 of varying degrees of reliability, and gave varying degrees of 

 information, exactly what species, or forms, to select for the 

 purpose. I decided to consider those only which I felt had been 

 determined with a considerable degree of accuracy, and which I 

 thought might be placed in one of three categories : first, living- 

 species now inhabiting the countries where the fossils are found: 

 secondly, exotic species belonging to the association which I have 

 termed ' the Chinese-North American association ' : that is. species 

 which are found in the countries of the Far East of Asia from 

 Japan to Malaya and Australia, including China, the Himalaj^a, 

 and Assam, or in North America, but do not now range into 

 Europe ; thirdly, exotic species of known genus which do not 

 belong to this association. 



I tried to keep a balanced judgment, but some parts of the 

 work were more fresh in mind than others, also it was difficult to 

 know always what to take and what to leave. There were species 

 about which I was undecided ; for though they were undoubtedly 

 exotic, sometimes the present range was not known. By excluding 

 them altogether the true proportion of the exotic element would 

 be distinctly under-estimated. It seemed best to include them 

 . and classify them merely as exotics, if the genus showed a con- 

 siderable European and Mediterranean distribution, and there was 

 no definite evidence to place them in the Chinese-North American 

 category. I am aware that this procedure is open to criticism, 

 but I tried not to force the evidence in any direction. The object 



1 E. M. Reid, ' Recherches stir quelques Graines Pliocenes de Pont-de-Gail 

 (Cantal) ' C. R. Soc. Geol. France, No. 6, Seance du 15 Mars, 1920. 



2 'Becouverte d'un Gisement Possilifere dans le Cantal' C. R. Acad. Sci. 

 Paris, vol. clxvii (1918) p. 534. 



