﻿100 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 8, 



products, it may be at least safely asserted that this is as probable an 

 origin as any other. 



We may safely conclude that the spot where the leaves are now 

 found, could not have been at any very great distance from at least 

 the border of the forest which yielded them. But it is probable that 

 the country on which it stood has foundered among the subsequent 

 convulsions, which seem to have broken and disjoined so many tracts, 

 once continuous. We may possibly even have a doubtful guess of 

 the direction in which that country lay. The headland of Ardtun 

 does not seem to bear any close relation to the rest of the traps, in 

 the same (southern) district of Mull. At a very short distance to 

 the east upon the southern shore, the terraces of trap are associated, 

 so far as yet examined, with no other formations than those of the 

 oolite and lias. From Macculloch's description, they both underlie 

 and overlie various members of those formations, in a manner very 

 similar to that in which the traps of Skye and many of the smaller 

 islands are found associated with the same series of rocks. The recent 

 observations of Prof. E. Forbes show, that in the case of Skye, this 

 association takes place in a manner which indicates with singular pre- 

 cision the age of some at least of the basaltic sheets (see page 108). I do 

 not believe that the higher basalts of the great precipices of the south 

 coast of Mull ever have been, or perhaps ever can be, examined with 

 very great minuteness. But no evidence certainly exists that any of 

 them are of later date than the secondary period; whilst the great differ- 

 ence of elevation renders it improbable that any of them can belong 

 to the same epoch with the Ardtun beds. I think the only indica- 

 tions of relation in the latter to any of the surrounding formations, 

 point in the northerly direction. No one who has followed the de- 

 scription of the Ardtun Head, and is acquainted with Staffa, will fail 

 to recognise a remarkably corresponding feature. The lowest two 

 members of the Ardtun series — the massive amorphous basalt, pass- 

 ing into and resting upon the columnar, — offer a precise representa- 

 tion on a smaller scale of that wonderful front which lies opposite at 

 some five or six miles' distance. It is to be observed too, that the 

 greater elevation to which these two formations rise in Staffa, corre- 

 sponds with the line of dip (rising to the north) of the same beds of 

 Ardtun. The whole group of the Treshnish Islands, " which guard 

 famed Staffa round," would seem from their low tabular appearance 

 to belong to the same prolonged sheets of trap, and may represent 

 the skeleton of that country now destroyed, from whose forests the 

 Ardtun leaves were shed. I think it not improbable that by future 

 researches among the conglomerates and other stratified matters as- 

 sociated with the traps in Mull and the neighbouring islands, portions 

 of the more substantial parts of those forests will yet be found. It 

 appears from Dr. Macculloch's account of the traps of the middle 

 district of the island of Mull, that he did actually find the carbonized 

 stem of a tree*, whose structure proved it to be coniferous. His 

 notice of the. "vein" in which it occurred is an accurate description 

 of the tuff which covers the leaves at Ardtun ; but he expressly says 

 * hoc. cit. vol. i. p. 568, and vol. iii. pi. 21. 



