ANNIVERSARY ADDRESS OF THE PRESIDENT. Ixxvii 



ever, we have distinct proof of the continuance of violent volcanic 

 action up to a date as late probably as the Middle Tertiary period. 

 This has been established by the discovery, by the Duke of Argyll, 

 of beds of Trap interstratified with tertiary and probably freshwater 

 strata. The phsenomena are described by his Grace in his paper 

 read before the Society, Jan. 8, 1851, and entitled " On the Tertiary 

 Beds of the Isle of Mull." It is accompanied by a " Note on the 

 Vegetable Remains from x\rdtun Head," by Prof. E. Forbes. 



The extreme south-western portion of Mull consists of a long pro- 

 montory, called the Ross of Mull, separated from the striking head- 

 land of Bourg, on the north, by Loch Scridden. It is deeply in- 

 dented on its northern side by Loch Laigh, which runs nearly north 

 and south. At the entrance of this loch, on its eastern shore, is the 

 headland of Ardtun, which presents the phsenomena forming the 

 subject of this paper. They consist of alternations of volcanic pro- 

 ducts with beds containing numerous and extremely well-preserved 

 vegetable remains, as shown in a small ravine, where alone the strata 

 are sufficiently accessible to be examined. The following beds occur 

 in descending order : — 



1. Basalt, taking the form of rude pillars, about 16 feet thick. 



2. The first leaf-bed, consisting of shaly matter, about 2 feet thick, 

 and containing impressions of leaves and stems of plants. 



3. A bed of volcanic ashes or tuif, 8 feet thick ; being an ashy 

 paste, full of white angular fragments or lapilli, for the most part 

 siliceous. It has one great peculiarity. The whole of the beds are 

 nearly horizontal, but dip slightly to the S.E., and in that direction 

 the bed passes into a conglomerate of flints cohering by an exceed- 

 ingly tenacious cement. One of these flints, found by the Duke of 

 Argyll, not only possessed the appearance of a chalk-flint, but was 

 also found to contain a fossilized organism, aifording unequivocal 

 proof of its origin. 



4. The second leaf-bed, by far the richest in vegetable remains. 

 It is about 2J feet thick ; its lower part consisting almost entirely of 

 a compressed mass of leaves. A few impressions of twigs are found 

 even in the superincumbent bed of tuff. 



5. A bed of tuff, similar to the one above mentioned, and 6 feet 

 thick. 



6. A seam of baked clay or fine mud, containing a few imperfect 

 impressions of leaves, apparently similar to those of the superior beds. 

 It is about 1-^ foot in thickness. 



7. A dark, amorphous, amygdaloidal basalt. 



8. Columnar basalt, descending beneath the sea-level. 



The thickness of the two last-mentioned basalts can be better esti- 

 mated a short distance east of the ravine, where they are respectively 

 48 and 10 feet thick. The superior volcanic beds are there thicker 

 than at the ravine, the leaf-beds retaining the same thickness. 



The author deduces several interesting conclusions from these phse- 

 nomena. The leaves belong to existing families of the Dicotyledonous 

 order ; they consequently belong to the Tertiary period, and Prof. 

 E. Forbes is disposed to refer them to the Miocene epoch. This 



