AND GRAVELS OF AEDTDN, ETC., EST MULL. 



285 



of the columnar flows hitherto seen. The lowest beds of amygda- 

 loidal basalt at Burgh or Carsaig are in fact quite 300 feet from 

 the base. The flows are also thickened and irregular on the shore 

 opposite Ulva and in Eorsa, as if they had been piled up against the 

 ridge, and they only become regular in Ulva itself and Gometra. 

 Farther, the ridge together with some of the first flows of Trap 

 must have formed a lake-basin, for from the shore of Loch Tuath to 

 that of Loch na Kael, a distance of over 2 miles, there are beds of 

 bole and lithomarge, at least a dozen feet thick and pisolitic in 

 places, cropping out among the basalts at heights of 100 feet or less 

 above the sea. The beds are continuous and distinctly laminated, 

 and the glacial beds over them are full of their fragments. These 

 must have been formed in a small lake-basin ; but I saw no trace of 

 any gravels except the glacial beds, which everywhere cling to the 

 sea-slopes, nor any beds which presented evidence of a fluviatile 

 origin. The course of the Ardtun river was therefore clearly not in 

 this direction, and must have been to the south of Gometra. I was 

 unable to explore the basalts round the north-west coast of Mull, 

 but do not anticipate that any important beds of sedimentary origin 

 would be met with. 



Before leaving the district, however, I visited the sections on 

 Loch Aline referred to by Prof. Judd (Q. J. G. S. vol. xxxiv. p. 734), 

 where it seemed possible that plant-remains might be discovered. 

 That part of the section between the gneiss and the columnar trap 

 at Beinn nah Uamha (Beinn y Hun, I. c.) was everywhere obscured 

 by talus ; but the section at the south-east angle of Beinn Iadain was 

 visible and substantially as described by Judd, except that the 

 " Chalk," as at the Wilderness by Burgh, is not bedded, but remanie 

 flints and chalk rubble only 4 feet thick. It does not appear to my 

 mind to be sufficient to furnish absolutely convincing evidence that 

 the sands beneath are of Cretaceous age ; but it is a question foreign 

 to our immediate subject and one which requires further investiga- 

 tion. 



Though it is quite obvious that the sedimentary beds at Ardtun, no 

 less than at Carsaig, are the ordinary gravels and muds of a river- 

 channel, important differences between them become apparent when 

 they are compared. At Carsaig their fluviatile character was at 

 once recognized by Prof. Judd; but those at Ardtun were believed 

 by such experienced observers as Sir C. Lyell, Mr. Smith of Jordan 

 Hill, and the Duke of Argyll to have had a volcanic origin. The 

 examination which led to this conclusion was made, however, in a 

 ravine where they appear to have been greatly affected by the 

 passage of a dyke, and where their peculiar weathering and dark 

 colour give them a truly volcanic aspect. On the sea front the 

 current-bedding is as plain as in the river-gravels of England, and 

 the block exhibited to the Society suffices to remove any doubt as to 

 their true nature. At Carsaig we find a conglomerate of boulders of 

 Trap and large flints resting directly on a Trap floor in one part of the 

 section, flanked on the west by silts, and overlain by a vast mass of 

 subangular flints of all sizes, scarcely even roughly sorted, the whole 



