AND GEAVELS OF ARDTUN, ETC., IIS T HULL. 



283 



feet above them, however, is a disturbed bed of black shale, 

 resembling that of Ardtun, from 1 to 2 feet thick, resting on thin 

 laminated sand formed of angular quartz grains, which can be traced 

 for a considerable distance, without, however, containing any plant- 

 impressions. The beds rise very rapidly, and this shale is soon 310 

 feet above the beach, whilst about a quarter of a mile further on the 

 top of the sandstone regarded as Cretaceous suddenly appears *, 

 220 feet above high water, thus occupying the horizon at which we 

 might have looked for a continuance of the flint gravels f. 



The headland of Burgh rivals the Innimore of Carsaig in grandeur 

 of scenery, its cliffs even surpassing the latter in height, and forming 

 an almost vertical escarpment of Traps, which for some distance 

 exceeds a thousand feet in depth. It presents the usual alternations 

 of columnar and amorphous, amygdaloidal and rudely columnar 

 flows, with intrusive sheets of dense Traps with starch-like jointing. 



At the base there appears to be an extensive ash-bed, and 

 directly over this columnar basalt, on the same horizon and probably 

 the same flow as that of Ardtun and Staffa ; above this is a bed 

 of dark, loamy, unfossiliferous sand, marking apparently the horizon 

 of the leaf-beds J. This is 3 or 4 feet thick, and includes clays, in 

 places, with vegetable matter. Above the leaf-bed horizon is rudely 

 columnar basalt as at Ardtun and Carsaig ; then amorphous trap 

 with a few included flints and other stones ; and then a massive 

 flow of Trap, over 70 feet in depth. Above this, again, are several 

 hundred feet of Traps, without any ash-beds, which latter do not 



* [Composed of quartz grains, for the most part very angular. — G. C] 

 t In the absence of proper horizontal measurements, which I did not at the time 

 realize were so important, it is impossible to ascertain the true dip; but 

 assuming the extreme points mentioned to be half a mile apart, roughly 

 plotted, it appears not much less than 5° or 6°. The beds, whether viewed from 

 the sea or the shore, do not indicate to the eye such a dip, and the horizontal 

 terracing of the cliff on the landward side equally negatives it. If the dip 

 does exist, the base of the flint gravels would be nearly 150 feet above the top 

 of the Cretaceous Sandstone. A much more accurate description of the Carsaig 

 section is needed, for it abounds in interest. Among the more striking objects 

 in the volcanic rocks is a layer or, more probably, the filling-in of a wide 

 fissure, consisting of great angular blocks of quartz and quart zite, the larger of 

 which must weigh at least a ton, and perhaps even several tons. Mr. Cole and I 

 first saw it on the sea-level some distance west of the Arches, where it looked like 

 an Archaean conglomerate ; but as it reappears high up the cliffs to the east, and 

 can there be seen filling crevices in the basalt, it is clearly of later date. A small 

 dyke not far distant has exactly the appearance of bedded sandstone. Behind 

 Beinn an Aoinidh, at about 700 feet elevation, there is a considerable quantity 

 of lignite, and a hundred feet lower, graphite is said to occur in the bed of a 

 stream, though when I visited the spot, properly guided, we failed to find any. 



} A large trunk of a coniferous tree, 5 feet in diameter, perhaps Podocarpus, 

 has been enveloped, as it stood, in one of the flows of Trap to the height of 40 feet. 

 Its solidity and girth evidently enabled it to resist the fire, but it had decayed 

 before the next flow passed over it, for its trunk is a hollow cylinder filled with 

 debris and lined with the charred wood. A limb of another, or perhaps the 

 same, tree is in a fissure not far off. Macculloch, who was certainly a most keen 

 observer, did not overlook this tree, which he described in 1819 in his 'Western 

 Isles of Scotland,' vol. i. p. 368, pi. xxi. fig. 1. The trunk was thought to be in 

 a vein of conglomerated fragments of Trap imbedded in a paste of the same. 

 He had also ascertained the wood to be coniferous. 



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