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



quently washed away ; or they may have been rolled by currents 

 from a distance and thrown by volcanic agency on the top of basalts 

 belonging to a former epoch. But I think the most probable con- 

 jecture is that, if these basalts do not even now rest upon chalk, they 

 have burst through it, and belong to the same period as the corre- 

 sponding beds of the Antrim coast. At all events it is clear that the 

 tertiary volcanos which at Ardtun give such clear evidence of inter- 

 mittent action, have been in a state of still more tremendous activity 

 on the neighbouring coast ; and were powerful enough to produce 

 repeated sheets of basalt of a thickness greater than, and of a form 

 very similar to, those on which the leaf-beds rest. 



It will be very singular if the comparatively thin sheet of basalt 

 which overlies those beds is the only one in the Hebrides which can 

 be proved to belong to the same period. It would in this case occupy 

 a position of very remarkable isolation ; the nearest basalts of the 

 same period being at a distance of not less than 75 miles, with inter- 

 vening islands, which do not exhibit any development of the trap 

 formation. It is however but a new proof in support of a geological 

 conclusion of much interest, viz. that the basalts of the Hebrides, as 

 we now see them, are the accumulated results of plutonic and vol- 

 canic action going on from time to time during an indefinite series of 

 ages, — and frequently not only at immensely distant points of time, 

 but also within very limited areas. 



Dr. Macculloch intimates, that he could observe very little corre- 

 spondence between the beds of trap, even in islands very near each 

 other, although a large number of them over all the islands from 

 Skye to Mull, seem to be referable to periods included in the oolitic 

 and the liassic epochs. Not unfrequently it has been observed by 

 the same writer, that many successive beds of trap rest upon, and 

 include conglomerates consisting chiefly of water-worn remains of the 

 same material ; thus indicating that some of the intervals had been 

 long enough to witness vast physical changes — the submergence, de- 

 struction, and reaggregation under water of still older rocks of the 

 same formation. 



I have very lately had occasion to observe on the coast of Kintyre 

 columnar basalt, which seems to have risen through the old red sand- 

 stone whilst the latter was yet in the state of sand, each column 

 being separated from the next on all its facets by cakes of sandstone, 

 now highly crystallized and very brittle ; but which, when in a state 

 to follow such labyrinthian lines, must have been soft and plastic. 



Before concluding this paper, I may mention that my attention 

 has been drawn by Prof. Nicol to a post-tertiary leaf-bed in Kintyre, 

 which has been discovered in cutting an outfall drain through the 

 flat area called the Laggan. In respect to the manner of deposit, 

 this bed presents a remarkable identity of character with the leaf- 

 beds of Ardtun. It consists of a mass of leaves, fully expanded and 

 mixed with very little mineral matter, associated with reedy plants ; 

 the whole still preserving the colours of damp leaves, and, although 

 very rotten, much of their original texture. They have evidently 

 been collected in the same manner — in a shallow marsh, and are 



