THIS Volume of the System of Mineralogy is to be viewed as a Sketch of the Science of Geo gnosy, in its present state. It contains a statement of the best ascertained facts respecting the aspect of the Surface, and the Structure of the Crust of the Earth, and a few inferences, which appear to he legi timate, with regard to their mode of formation. It is intended also as the Text Book for my Lectures on Geognosy. R. J. CON-