If Lamarck allowed his brilliant faculty of generalisation to lead him far astray in his opinions regarding the origin of rocks, he bad formed a saner judgment on the causes that have developed the present terrestrial topography. The first chapter of the “Hydrogéologie ” is devoted to a consideration of the natural results that arise from the circulation of water over the surface of the land. This subject, he remarks, affords less scope than any other for the exercise of the imagination in framing hypotheses, for it can be studied on a basis of facts which are generally familiar. Though the question required to be considered in his treatise and was capable of easy solution, yet it seemed to him to be novel, at least from a general point of view, and to have been previously neglected by physicists and naturalists. He appears to have formed his conclusions regarding it independently, and to have been unaware how far he had been anticipated by previous observers. It is singularthat he makes no allusion to the work of his distinguished fellow-countryman Desmarest, who some thirty years previously had demonstrated, from a prolouged and minute investigation of the volcanic history of Auvergne, that the valleys of that region have been excavated by the streams which flow in them. He does not refer to the enunciation of the same doctrine by De Saussure a few years later in regard to the valleys of the Alps, nor to the clear presentation of similar views by Hutton, whose system had been expounded to French readers by Desmarest. But though he was mistaken in supposing that the doctrine was novel, Lamarck was not surpassed by any of his predecessors in the firmness with which he espoused it, and in the clearness with which he presented it to the world.