Sir George Mackenzie read a paper on the Theory of the Parallel Shelves in the Glens of Lochaber, in which he first noticed the objections to the theories that ascribed the origin of these appearances to fresh-water lakes, the barriers of which had been destroyed at different periods; and to the ordinary action of the sea when the land was at a lower level than at present. The causes supposed to have removed the barriers, in the first case, being violent disruptions, the preservation of level and parallelism is totally inconsistent with such operations.