412 Mr. J. Starkie Gardner. Fossil Plants and the [Dec. 17, 



II. " Second Report on the Evidence of Fossil Plants regarding 

 the Age of the Tertiary Basalts of the North-East Atlantic." 

 By J. Starkie Gardner. Communicated by Sir J. D. 

 Hooker, K.C.S.I., F.R.S. Received November 30, 1885. 



I have the honour to make known the results attending the expen- 

 diture of £75, placed in my hands by the Government Grant Com- 

 mittee for the purpose of investigating the fossil floras of Scotland, 

 which has been expended at Ardtun Head. 



The position and physiography of this headland in the Isle of Mull 

 has been fully described by the Duke of Argyll. It is the point of 

 land separating Loch Laigh and Loch Scridain, and is about two 

 miles in circumference and a mile across. 



It is composed mainly of two sheets of basalt with remains of a 

 third sheet, on some eminences and along the shore of Loch Laigh. 

 These are almost horizontal, with a slight dip east, up Loch Scridain, 

 and a considerable dip in the same direction up Loch Laigh. The 

 upper sheet is not less than 40 to 50 feet thick, crystallised into rude 

 massive columns, now much fissured and weathered, whilst the 

 lowest presents a thickness of 60 feet, visible above low water, the 

 upper two-thirds being amorphous, and the rest fashioned into slender 

 and most perfect columns, bent in every direction, like those of the 

 Clam-shell cave at Staffa. The beds are so exceedingly horizontal 

 towards the seaward direction, that no one can doubt the columnar 

 basalts of Staffa and the Treshnish Isles, Geometra and the mainland 

 of Mull, being on the same horizon, if not parts of the same sheet. 

 Between the two great lava beds at Ardtun is intercalated a bed of 

 sedimentary deposit, reaching a maximum of 60 feet thick, and con- 

 sisting of pale very fine-grained clay and limestone at the base, then 

 sand and gravel, black laminated shales, whinstone, gravel, and 

 laminated sands. The gravels are made up of flint, pebbles, and 

 subangular rolled fragments of older lava beds, in a matrix of broken- 

 down volcanic material. They present all the ordinary lines of 

 current bedding, beautifully weathered oat, and the pebbles are 

 drifted precisely as in ordinary river gravels. 



There can be no question whatever, indeed, but that the gravels are 

 the deposits of the waterway of a river, and the shales, its overflows 

 and backwaters. The river must have been of some magnitude, as 

 its deposits traverse the whole seaward face of the headland, and their 

 extension inland seems to be marked by the occurrence of two beds of 

 coal, which have, to a small extent, been worked, one near Bunessan 

 and the other nearer Ardtun village. An intrusive sheet of fine 

 compact basalt rises on one side of the head, cutting a devious waj~ 



