100 BRITISH EOCENE FLORA. 



parent like the veins. The veins are very well defined and slightly elevated on the under 

 side of the leaf (figs. 1 and 3, PI. XXV), but less easily traced on the more wrinkled 

 upper surface, figs. 2, 4, 5. The latter figures exhibit the undulations or folds such as 

 are frequently seen in the leaves of the living tree. 



The specimens from the newly noticed bed at Ardtun are far larger and better pre- 

 served than any previously found in Tertiary Rocks. In a layer of white clay at the base 

 of the bed they are of a purple colour and massed together in the greatest profusion. The 

 specimen (fig. 3) is from this layer and shows the texture, after maceration, to have been 

 such that the venation of an immediately underlying leaf is distinctly visible through the 

 one above. 1 They are much larger than the average in the living species, if we may 

 judge from dried specimens and those in cultivation, but a garden variety has been 

 produced in France in which the leaves often measure five and even six inches across. 2 



The Ginkgos are very large trees indigenous to China, where they seem, however, 

 as yet to be unknown in a wild state. When stripped of their leaves there is 

 nothing to indicate, externally, that they belong to the Coniferse. The peculiarities of 

 their internal structure and a brief sketch of their ancestry are described on pp. 45 and 

 122 of this memoir. 



There can be no reasonable doubt about the specific identity of the Ardtun fossil and 

 the living G. biloba, Linn., yet as only the foliary organs of the former are known, 

 we should hardly be justified in making it an exception to the rule which has hitherto 

 conferred distinct specific names on plants of Eocene age, no matter how great their 

 resemblance to existing species may be. We can hardly admit the identity of the 

 magnificent Scotch species with the starved Cretaceous form from Greenland, to which 

 the name G. primordialis, Heer, was applied : but we cannot regard the British form as 

 distinct from Ginkgo or Salisburia adiantoides, Ung., 8 though the largest of the specimens 

 figured by either Heer or Massalongo under that name do not equal in size those shown 

 on PI. XXV. When, however, a trinomial system is adopted, as must some day happen, 

 its full name might well be G. biloba hebraidica, with the addition oifoss. or/, for fossil, 

 thus rendering any confusion impossible. 



I had never heard that Ginkgo occurred in Mull, until I found a few imperfect 

 specimens this year in the black beds of Ardtun ; but its presence had long been known 

 to the Duke of Argyll, who had, indeed, for many years, possessed a specimen in his 

 Museum at Inveraray. It is, as already stated, abundant in the light-coloured beds of 

 Ardtun, and the fact that this singular tree flourished within the British area in Tertiary 

 times should be of some interest to botanists as well as geologists. 



1 The leaves, though leathery when freshly gathered, become relatively thin when pressed, and 

 underlying leaves can be seen through them, as in the case mentioned above. 



2 Gordon's Pinetuni, S. adiantifolia macrophylla, Hort., p. 3/5, 1880. 



3 It abounds chiefly, it appears, at Hare Island, a few miles north of Disco, and at Atanekerdluk. 

 Heer has also noticed fragments from the grey clays of Samland, on the Baltic. 



