ANNIVERSARY ADDRESS OF THE PRESIDENT. 1 65 



the mainland of Scotland there was a copious outpouring of lava in 

 numerous successive flows, until wide tracts of country were buried to 

 a depth of sometimes more than 3000 feet. These lavas are gener- 

 ally dolerites and basalts, both with and without olivine, while some 

 less basic varieties may be classed as andesites. They lie as out- 

 spread sheets from not more than 6 or 8 feet to 80 or 100 feet in 

 thickness, showing sometimes a perfect columnar structure, some- 

 times weathering as dull greenish amygdaloids. 



The fragmeutal rocks associated with these bedded lavas are com- 

 paratively insignificant in amount. They occasionally occur as 

 well-marked bands of fine tuff separating the basalts, as in the well- 

 known cliff-section at the Giants' Causeway. Elsewhere they appear 

 as volcanic conglomerates or as coarse breccias, occasionally made up 

 largely of non-volcanic materials. Of this last character are the 

 remarkable breccias of Sgurr Dearg in ]\Iull, which contain enormous 

 masses of mica-schist, one such mass measuring 100 yards long by 

 30 yards wide. 



Among the fine tuffs, and occasionally in cavities between two 

 sheets of basalt, lenticular seams of lignite and even of true coal 

 may be observed. Prom the detached leaves and fruits so well 

 preserved in some of these tuffs and other associated deposits it is 

 clear that the vegetation was terrestrial. The eruptions are thus 

 recognized as subaerial. On successive lava-fields hollows arose in 

 which water gathered, and into the pools and lakes thus formed 

 leaves from the surrounding woodlands were blown or washed. 



From the evidence of the fossil plants thus preserved, it may be 

 inferred that the eruptions took place in older Tertiary time. More- 

 over, in some places the lowest basalts lie unconformably on 

 Cretaceous rocks, or on conglomerate mainly made up of fragments of 

 chalk and flints. Hence, both palaeontological and stratigraphical 

 evidence agree in indicating that the date of the volcanic outbursts 

 of Antrim and the Inner Hebrides must be placed after the end 

 of Mesozoic time. 



Some of the vents of eruption whence these lavas were emitted 

 can be detected on the plateaux and on the older rocks lying outside 

 of them. They are less numerous than, for instance, those con- 

 nected with the Carboniferous plateaux, though this comparative 

 infrequency may be partly due to the fact that, save in Antrim, the 

 geological structure of the ground has not yet been worked out in 

 the same detail as the Carboniferous regions. Certain prominent 

 bosses of basalt and dolerite rising out of the bedded basalts doubtless 

 mark the sites of eruptive vents belonging to a late part of the 



VOL. XLVIII. m 



