Having listened with much pleasure to several able lectures on Geology and Palæontology which have already been delivered in this Hall, I believe I am correct in affirming, that the general tendency of these discourses has been altogether in one direction; the object being, to impress forcibly upon your minds the opinion that the various changes which have taken place in the earth's history, inhabitants, and surface configuration, have been mainly effected by what may be termed external agencies, i.e., by forces acting from without, slow but sure in their operations, yet but comparatively so feeble in their energy as to demand a practically unlimited amount of time being placed at their disposal to enable them to accomplish those great revolutions which we see and know to have taken place in the geological history of our globe.