In his ‶Text-Book of Geology,″ Dr Archibald Geikie states that many years ago, Mr Godwin Austen held that the numerous basins, in which the Old Red Sandstone formation was laid down, had been inland lakes or seas; and that this view had been sustained by the late Sir A. C. Ramsay. He proceeds to define the one which he (Dr Geikie), for convenience, calls Lake Caledonia, as occupying the valley between the base of the Highland uplands and those of the southern counties. On the north-east it is cut off by the present coast-line from Stone-haven to the mouth of the Tay. On the south-west it ranges by the Island of Arran across the Channel into Ireland, where it runs almost to the western seaboard, flanked on the north, as it is in Scotland, by the Crystalline Rocks, and on the south by the Silurian Belt. In this basin the lower series of deposits attains a maximum thickness of 20,000 feet. The accumulation of so great a thickness can only be explained on the supposition that the subterranean movements, which at first ridge up the silurian sea-floor into land, enclosing separate basins, continued to deepen these basins, until enormous masses of sediment had slowly gathered in them; and that there are proofs that this subsidence was interrupted by occasional local elevations. In his book on the Scenery and Geology of Scotland, Dr Geikie, in writing of this valley, remarks that it is only in the broad sense, as a band