General Introduction The Highlands of Scotland have long been recognized as an unrivalled field of study for the physical geologist; but to the stratigraphical geologist and the palæontologist, who seek for evidence to aid them in reconstructing the geographical features and determining the biological characteristics of successive geological periods, they have, till of late years, been regarded as comparatively barren of interest. An exception to this general statement must be made, however, in favour of the Old Red Sandstone of the district, which has yielded such admirable results to the studies of Murchison, Sedgwick, Malcolmson, Hugh Miller, Agassiz, and others. Charles Peach's discovery in 1854 of Silurian fossils in Sutherland has already borne the most important fruit, and, in the hands of Murchison, Ramsay, Geikie, Harkness, and Jamieson, has afforded the necessary clue for determining the age of the great Primary masses of the Highlands. Similarly the discovery by the Duke of Argyll of Miocene vegetation in beds intercalated with the basalts of Mull has been the starting-point in elucidating the history of the Tertiary period in the Highlands. Professor Geikie has already laid before this Society the first of a series of papers in which he proposes to treat this interesting subject. The Secondary strata of the same area were, at so early a period as 1826, made the object of an admirable general survey by the late Sir Roderick Murchison; but the progress of geological science since that date appears to create a demand, and at the same