CHAPTEE XIX 
AmCAXOES OF THE LOWER OLD RED SANDSTONE OF “LAKE CALEDONIA” 
Description of the several Volcanic Districts : “Lake Caledonia,” its Chains of Volcanoes 
— The Northern Chain : Montrose Group, Ochil and Sidlaw Hills, the Arran and 
Cantyre Centre, the Ulster Centre. 
I NOW propose to give some account of each of the districts which liave been 
separate areas of volcanic action during the time of the Lower Old Eed 
Sandstone, tracing its general structure, the arrangement and sequence of its 
volcanic rocks find the history of its eruptions. As bj" far the most varied 
development of the Old Eed Sandstone is to be found in the great Midland 
Valley of Scotland, and as it is there that the remarkable volcanic phenomena 
of the system have been most abundantly displayed and are most clearly 
recorded, I shall begin my description of the volcanic eruptions of the Low'er 
Old Eed Sandstone witli a detailed account of the different centres of 
volcanic activity in that region. The phenomena are so fully displayed there 
that a more summary treatment of the subject will suffice for the other 
regions. 
Linder the designation of “ Lake Caledonia,” as already remarked, I 
include the wdiole of the Midland Valley of Scotland between the Highlands 
and the Southern Uplands, likewdse the continuation of the same ancient 
hollow by Arran and the south of Cantyre across the north of Ireland to 
Lough Erne.^ Throughout most of the area thus defined, the present limits 
of the Lower Old Eed Sandstone are sharply marked off by large parallel 
faults. On the north-west side one, or rather a parallel series, of such dis- 
locations runs from Stonehaven along the flank of the Highland mountains 
to the Clyde, thus traversing the wdiole breadth of the i.sland. On the 
^ My own investigations of this region have been continued over an interval of forty years. 
Besides personally traversing every portion of it, I have mapped in detail, for the Geological Survey, 
many hundreds of square miles of its area from the outskii'ts of Edinburgh south-westwards into 
Lanarkshire, in Ayi'shive, and in the counties of Fife, Perth and Kinross. The Geological Survey 
maps of the volcaiiie tracts of the Sidlaw Hills have been prepared by my brother, Prof. James 
Geikie, and Messrs. H. M. Skae and D. R. Irvine. The W'’estern Ochils were mapped chiefly by 
Mr. B. N. Peach, partly by Prof. J. Young, Mr. E. L. Jack and myself; the Eastern Ochils 
were surveyed mainly by Mr. H. H. Howell ; while the volcanic belt between the tracts mapped 
by me in Lanarkshire and in Ayrshire was chiefly traced out by Mr. Peach. As a rule, each of 
these geologists has described in the Survey Memoirs the portions of countiy surveyed by him. 
