Having briefly noticed the topographical features of the island, the author pointed out, by means of a map and sections, the relative positions of the sedimentary rocks. He described in detail the sedimentary deposits on the south side of the island, and then gave a transverse section of them, from Port-na-Haven on the west to Port-Askaig on the east. Although the rocks in the central valley of the island had not yet yielded identifiable organic remains, he did not despair, if properly investigated, of forms being found that would place them beyond doubt in the Lower Silurian series. In mineral character, they quite coincided with those described by the late Sir Roderick Murchison as occurring in Ross and Sutherland shires. On the east side of the island, at Port-Askaig, these deposits repose upon a series of stratified rocks of much higher antiquity, which correspond to the Cambrian rocks of the North-west Highlands described by the same distinguished author. At the base of these latter sedimentary rocks there is a mass of conglomerate made up of fragments and boulders of granite, embedded in an arenaceous talcose schist; and as no granite occurs in situ in the island, he was disposed to account for its presence in this conglomerate by the agency of ice. Specimens of the granite and a striated block of quartzite were laid upon the table. He then described the rocks of the western extremity of the island, which consist of highly-metamorphosed stratified rocks—as gneiss, serpentine, dolomite, quartzite, and This 250-word extract was created in the absence of an abstract