ANNIVERSAlir ADDRESS OF TDE PRESIDENT. 65 



kind, but the subject deserves, and, if life and opportunity be allowed 

 me, will before long receive, fuller treatment. 



I. Distribution oe Volcanic Districts. — The area within which 

 volcanic rocks belonging to the Old Hed Sandstone appear is one of 

 the most extensive regions over which the volcanic eruptions of any 

 geological period can be traced in the British Isles. Its northern 

 limit reaches as far as the islet of Uya in Shetland, and its southern 

 appears in England in the Cheviot Hills — a distance of about 250 

 miles. But volcanic rocks of corresponding age occur even as far 

 to the south as the hills near Killarney. The most easterly margin 

 of this area is defined by the ]N"orth Sea oh the coast of Berwickshire, 

 and its extreme western boundary extends to near Lough Erne in 

 the north of Ireland — a distance of some 230 miles. If we include 

 the Devonian volcanic rocks as contemporaneous with those of the 

 Old Red Sandstone, the area of eruption will be greatly enlarged, so 

 as to include the diabases and tuffs of Devon and Cornwall. But 

 leaving the latter out of account for the present, and confining 

 our attention to the Old Eed Sandstone series, we find that within 

 the wide limits over which the volcanic rocks are distributed a 

 number of distinct and often widely separated centres of eruption 

 may be traced. Taking these as they lie from north to south we 

 may specially enumerate the following : — 



1st. The Shetland and Orkney Islands, including probably several 

 distinct volcanic groups of which the most northerly extends through 

 the centre to the north-western headlands of the mainland of Shet- 

 land, while another lies in the island of Shapinshay, one of the 

 Orkneys. 



2nd. The Moray Eirth, embracing probably several scattered vol- 

 canic vents. One of these occurs near Buckie, on the coast of 

 Banff'shire ; another at Gartly and Strathbogie, in the west of 

 Aberdeenshire. 



3rd. The basin of Lome to the west of the mainland of Argyll- 

 shire, extending from Loch Creran to Loch Melfort and the hills on 

 the west side of Loch Awe. 



4th. The great central basin of Scotland, which, for the sake of 

 distinctness, I have called ^ Lake Caledonia,' ^ stretching between 

 the edge of the Highlands and that of the Southern Uplands from 

 the east coast south-westwards across Arran and the south end of 

 Cantire into Ireland as far as Lough Erne. I^umerous separated 



1 Trans. Eoy. Soc. Edin. vol. xxviii. (1878) p. 354. 



