104 



BRITISH EOCENE ELORA. 



mass is composed of some four and twenty horizontal sheets of lava of great thick- 

 ness, and furnishes the key to the position of the Ardtun and Staffa beds in the series, 

 for Cretaceous and Jurassic rocks crop up at its base. The eruptive series commence with 

 two great deposits of ash, each twenty or thirty feet thick, followed by some 100 feet of 

 lava, the upper bed of which seems part of the flow forming the beautiful columnar beds 

 of Ardtun and Staffa. An interval of rest followed, during which the fluviatile beds of 

 Ardtun were deposited ; these being represented at Bourg by nine to twelve feet of clays 

 and sand without fossils. They are overlain by a bed of rudely columnar Basalt, identical 

 with that which overlies the leaf-beds and forms the capping at Ardtun. Next is a bed 

 of scoriaceous lava, thirty feet thick, which has caught up a few flints, and a bed seventy 

 feet thick of remarkably compact lava. Above this again is about 1000 feet of lavas, 

 some very much decomposed, with little if any intervening ash-beds, only a few thin 

 beds of which reappear towards the summit. 



It can hardly be doubted, in view of their great horizontal extent and vertical 

 thickness, that nearly the whole of these lavas were formerly continuous, for no less 

 majestic cliffs of the same composition form parts of coast lines east and west, and north 

 and south. Time, however, has not spared them, and scarcely anything now remains 

 at Ardtun and the Isles of all the long series of flows, except portions of two of the 

 lowest and oldest sheets. The under part of the inferior of these is transformed into such 

 columns as those which have made Staffa famous, though they are no less beautiful at 

 Ardtun ; while the upper one, imperfectly columnar and much fissured and jointed, forms 

 still more precipitous and picturesque cliffs, presenting the appearance of ruined masonry. 

 Sandwiched between these is a mass of sedimentary rock which reaches a maximum 

 thickness of over thirty feet. A small chine or ravine marks almost the centre of the 

 headland, and it was here that the Duke's published sections were taken. The eastern 

 face is the more accessible and best to work, and it was at this spot that I decided to 

 carry on somewhat extensive quarrying operations, whereby the following beds were 

 penetrated. Resting upon the amorphous Basalt is a bed of carbonaceous rubble filling 

 in the inequalities of the lava and about a foot thick, succeeded by two feet of indurated 

 sand or grit. The true leaf-bed, the second in the Duke's section, follows ; and though 

 now a hard and brittle black shale, was originally a fine carbonaceous mud. It is two 

 feet four inches in thickness, the lower part squeezed and without recognisable fossils ; then 

 a few layers containing numerous specimens of a simple ovate leaf;^ another layer 

 squeezed and with only macerated remains, and finally some layers made up almost 

 wholly of large palmate leaves, known as Platanites aceroides. Overlying this, and 

 distinctly separated, is a bed, a foot thick, of very hard whin-like rag, doubtless sandy 

 carbonaceous mud when deposited, containing very large leaves of the so-called Platanites, 

 with broken up fronds of Onoclea and Ec[uisetum. The next bed is similar, marked 

 off by a definite plane of bedding. It possesses few if any fossils, and passes gradually 

 ^ Bhamnites, Forbes, in the Duke of Argyll's Memoir. 



