President's Address. 11 



of the areas of deposit, while the Highland tableland either 

 remained stationary or formed an axis of elevation. The 

 great succession of conglomerates, sandstones, and shales, 

 amounting to 20,000 feet in thickness, is composed more or 

 less of the ddhris of the crystalline rocks of the Highlands ; 

 even the pebbles in the conglomerates of Uamh Var, which 

 form the hiohest members of the Lower Old Eed Sandstone 

 of the Midland valley, have been derived from areas of crys- 

 talline rocks not far removed from the Highland barrier. 

 The latter fact leads us to infer that portions of the old 

 tableland still remained above water towards the close of the 

 Lower Old Eed Sandstone period. From an examination of 

 the physical relations of the strata along the Highland 

 border, it is manifest that there must have been irregular 

 subsidence of the land along the northern margin of the 

 midland basin. For example, on the shore at Stonehaven, 

 nearly 5000 feet of sandstones, flags, and shales underlie the 

 great volcanic series so splendidly developed in the Sidlaws 

 and the Ochils. But when we pass to the south-west of the 

 Stonehaven area into Forfarshire and Perthshire, this accumu- 

 lation of sedimentary deposits is overlapped by the represen- 

 tatives of the volcanic series, till the latter rest directly on 

 the ancient crystalline rocks. Although this vast thickness 

 of strata accumulated in a lake, it is evident that the depth 

 of water never could have been very great, for bands of con- 

 glomerate frequently occur in the order of succession, com- 

 posed of river-borne pebbles. Most of these have been 

 derived from the crystalline rocks of the Highlands, while 

 not a few are composed of the same materials as the ejecta- 

 menta of the Lower Old Eed Sandstone volcanoes, which 

 were situated either within the limits of the lake or along its 

 margin. On the western slopes of the Ochils, conglomerates 

 of great thickness are entirely made up of the rounded frag- 

 ments of the lavas and agglomerates of the adjoining range, 

 thus indicating that the volcanoes which were at first sub- 

 aqueous had reared their cones above the surface of the lake. 

 Owing to the gradual submergence of the area, they were 

 eventually submerged and buried underneath the accumu- 

 lating sediment. The remains of true air-breathing insects 



