THE BASALTS OF IKFLANT) ANT) SCOTLAND. 659 



question whether the fossil should be allowed to retain the specific 

 name given by Edward Forbes, who described it without being 

 aware of its close relation to an existing species : or whether we 

 should, follow Prof. Newberry, who has united a later and more 

 robust species, from North-American Tertiaries, with the living 

 one. The former course appears preferable, at least provisionally. 

 The pinna? are exceedingly variable as in the existing species, 

 both as regards their cutting and venation — fig. 1, from near the 

 base, and fig. 2, from the apex of a frond, representing two of 

 the extremes. The slender stipes, from 1 to 2 feet and more in 

 length, which are seen crossing some of the slabs recently 

 obtained from Mull, appear to be grooved and glabrous. The 

 fertile frond is identical with those of O. sensifiilis (fig. 4), except 

 that the sori are somewhat smaller (fig. 3). A soft texture is 

 indicated in the fragmentary state in which the fossil is usually 

 found, and the character of the impressions in the shale points 

 in the same direction. 



The discovery of this Onoclea at Mull is particularly interesting, 

 since it has as yet not been met with elsewhere in Europe. It is 

 limited to the upper layer, about a foot thick, of the black shaly 

 leaf-bed at Ardtun Head, where much macerated fragments occur 

 in some abundance, in company with a large palmate leaf, com- 

 pressed reeds, and Equiseturn. The bed is fluviatile, and seems 

 to have been formed alongside a river, in a swamp liable to inun- 

 dation, similar to the Tilbury flats before their level was raised. 

 The age of these beds has not been ascertained with any certainty; 

 but after a careful review of both the stratigraphical and pala?on- 

 tological evidence, I can no longer hesitate to regard their horizon 

 as at least as old as the Lower Eocene, and probably below that 

 of the Thanet Beds. 



The fossil Onoclea is not exclusively confined to Mull ; it has 

 also been brought from Atanekerdluk, in Greenland, by Mr. 

 Whymper, in an equally macerated condition. It was at first 

 named Woodwardites arcticus by Heer ; but Dr. Newberry subse- 

 quently pointed out its true affinity, and it is satisfactory to know- 

 that the identification of the Mull and Greenland specimens is 

 supported by one of the highest living authorities on fossil plants, 

 the Marquis de Saporta. Along with fragments with copiously 

 anastomosing venation, named JFoodwardites, are others of more 

 robust aspect and much simpler venation, originally named JPeco- 

 pteris Torellii, Heer, but afterwards corrected by Heer, first to 



