53 



would appear that such beds occur also in Skye and others of the 

 Western Isles. Similar conditions thus appear to have prevailed over 

 a very wide area, the successive eruptions of igneous matter over the 

 sea bottom were very similar, and there were like periods of repose, 

 during which the productions of the adjoining land were swept 

 down to be buried under the next flow of submarine lava. 



The wood which has supplied the Antrim and Mull lignites, has 

 been ascertained to be coniferous ; but the species have not been 

 determined. Mr. Eobert Brown and Professor Lindley referred the 

 former with some hesitation to one of two species the common fir 

 (Pinus Abies) or the Weymouth pine (P. Strobus); and Professor 

 Edward Forbes, who reported upon the Mull leaves, at the request 

 of the Duke of Argyle, found that they belonged to a taxus, a 

 platanus, and several species of rhamnites, upon which he did not 

 venture to pronounce positively (Jour. Geol. Soc., vol. vii., p. 103, 

 1851). The lignites which occur in Mull in a bed under basalt, 

 apparently in direct continuation of the leaf-beds, have been 

 recently submitted by Professors Harkness and Blyth to a micro- 

 scopical and chemical examination, and their structure compared 

 with that of the Causeway lignites (Ed. Phil. Jour., New Ser., iv., 

 p. 304, 1856). The results show that the variations from the ordinary 

 coniferous structure are the effects of the great pressure to which 

 they were subjected by the accumulation over them of thick beds 

 of igneous matter. We have failed, as already remarked, in deter- 

 mining the nature of the Bute lignite ; but it has quite the appear- 

 ance of being coniferous ; and the beds associated with it being 

 exactly the same as accompany the Antrim lignites, there is every 

 probability that both are of the same age. Now, the basaltic series 

 of the north-east of Ireland, as it overlies the chalk formation, 

 clearly belongs to the tertiary era, and was long ago recognized as 

 of this age. But many cases occur in which the same basaltic flow, 

 which alters the chalk to the state of a saccharine marble, spreads 

 out beyond the limits of the chalk, and overlies and alters the 

 new red sandstone and coal measures. Such overlying masses must 

 also belong to the tertiary period. It is therefore not improbable 

 that the basalts forming the lofty cliffs on the west coast of Mull, 

 superimposed upon the lias and oolites, may also be tertiary. The 

 Duke of Argyle is inclined to refer these to an older date ; while 

 his Grace, in the able and interesting paper above mentioned, clearly 

 shows that the Ardtun leaf-beds and lignites are of tertiary age. It 

 seems to us, however, to be premature to place these and the Antrim 

 lignites in the miocene group, as his Grace and Sir Charles Lyell 



