270 



MK. J. S. GA.RDNEE ON THE LEAF- .BEDS 



22. On the Leaf-beds and Gravels of Ardtun, Carsaig, <f*c, in 

 Mull. By J. Starkie Gardner, Esq., F.G.S. With Notes by 

 Grenville A. J. Cole, Esq., E.G.S. (Read January 12, 1887.) 



[Plates XIII.-XVL] 

 The Ardtun leaf-beds have once before formed the subject of a com- 

 munication to this Society *. Its author was the Duke of Argyll, 

 and its interest exceptional, as it once for all fixed the age of the 

 great Trap formation of the Inner Hebrides ; and geologists learned 

 that, even since a period so recent as the Tertiary, beds of most stub- 

 born rock, exceeding 1000 feet in thickness, had been denuded and 

 abraded until, over extensive areas, little more than the merest 

 vestiges of them remained. The value of this discovery to the geolo- 

 gist can hardly be overestimated, for the data then furnished ma- 

 terially assisted to determine the age of the Traps stretching from 

 Antrim to Greenland. 



The fossil plants, to which so much importance attached, were 

 briefly described in this paper by Edward Forbes, and all the most 

 characteristic forms were figured. He inclined to the idea that they 

 might be of Miocene age, but did not commit himself definitely ; 

 while the Duke of Argyll, even though author of the paper, refrained 

 from expressing any opinion. Prof. Heer, however, who was then 

 describing the Miocene flora of (Eningen, pronounced them to be 

 Miocene ; and the weight of his authority has been such, that no 

 serious attempt has ever been made to reexamine the evidence on 

 which his opinion was based. This ruling was extended to the 

 fossil plant-beds of Greenland, with the result that a vast series of 

 physical changes, which extended over the entire Tertiary period, 

 have been crowded into a single stage, the Miocene. It is 35 years 

 since the Ardtun flora was described, when the study of fossil plants 

 was so far in its infancy that the occurrence of Dicotyledons in Cre- 

 taceous beds was unsuspected, and even plants of Eocene age were 

 very imperfectly known. In the concluding part of this paper evi- 

 dence will be brought forward to show that it should actually be 

 placed very low down in the Eocene. 



The Ardtun beds are situated in Mull, long. 6° 13-14' W., and 

 lat. 56° 20-21' 1ST., in the promontory of Ardtun, between Loch na 

 Lathaich and Loch Scridain. The earlier observations are recorded 

 by the Duke of Argyll, and, since 1851, the beds and their fossils 

 have been continually referred to, particularly in text-books on geo- 

 logy and guides to the Western Isles ; but the spot itself seems to 

 have been little visited, and nothing has been added to the Duke's 

 descriptions. Much additional light has, however, been thrown on 

 the Trap-formation generally by the works of Professors Geikie and 

 Judd, and Dr. James Geikie f. 



* Quart. Journ. Geol. Soc. vol. vii. p. 89. 



t Prof. Geikie, Quart. Journ. Geol. Soc. vol. xxvii. p. 279, ' Nature,' Nov. 4, 

 1880, and elsewhere ; Prof. Judd, " On the Ancient Volcanoes of the High- 

 lands, and the Relation of their Products to the Mesozoic Strata," Quart. Journ. 

 Geol. Soc. vol. xxx. p. 220, and " On the Strata of the Western Coast and Islands 

 of Scotland," Quart. Journ. Geol. Soc. vol. xxxiv. p. 6G0. Dr. James Geikie, 



