66 PROCEEDINGS OF THE aEOLOGICAL SOCIETY. 



volcanic groups occur in this great basin, of which I shall give a 

 more detailed account. 



5th. The Cheviot basin, including the rocks of the Cheviot Hills 

 and others, probably independent, which are cut off. by the sea along 

 the eastern coast of Berwickshire between St. Abb's Head and 

 Eyemouth. 



6th. The Killarney tract, including the hills lying around Lough 

 Guitane in the east of County Kerry. 



At the outset I wish to call the attention of geologists to a 

 feature in the volcanic history of Britain which first comes out 

 prominently in the records of the Old Ked Sandstone, and appears 

 with increasing distinctness during the rest of the long sequence 

 of Palaeozoic eruptions. I allude to the persistence with which the 

 vents have been opened in the valleys and have avoided the high 

 grounds. I formerly dwelt on this relation with reference to the 

 Carboniferous volcanic phenomena,^ but the observation may be 

 greatly extended. With regard to the Old Bed Sandstone of Central 

 Scotland, though the lavas and tuffs that were discharged over the 

 floor of the sheet of water which occupied that region gradually rose 

 along the flanks of the northern and southern hills, yet it was on the 

 lake-bottom and not among the hills that the orifices of eruption broke 

 forth. 



So far as I am aware, no undoubted vents of the age of the Lower 

 Old Bed Sandstone have been detected among the high grounds 

 of the Highlands, although a fringe of the lavas may be traced here 

 and there along the base of the hills. In some cases, doubtless, the 

 position of the valleys may have been determined by lines of fault that 

 might well serve as lines of relief along which volcanic vents would 

 be opened. But in many instances it can be proved that, though the 

 vents have risen in valleys and low grounds, they have not selected 

 lines of fault even though these existed in their neighbourhood. I 

 shall have occasion to give illustrations of these statements in sub- 

 sequent parts of this Address. 



By far the most varied development of the Old Bed Sandstone is 

 to be found in the great Midland Yalley of Scotland. It is there that 

 the remarkable volcanic phenomena of the system have been most 

 abundantly displayed and are most clearl}' recorded. I shall there- 

 fore base my description of the volcanic eruptions of the Lower OldEed 

 Sandstone chiefly on the results of a study of that region, contenting 

 ^ Op. cit. vol. xxix. (1879) p. 454. 



