1. RANGE AND STRUCTURE OF THE CHALK FORMATION. Considered mineralogically, this rock can never fail to arrest attention or inquiries, even among the least observant, as to its nature and origin. There is no trace of it in the northern portion of the island; and when one for the first time sees whole mountains of it, his sensations are not a little exciting. For our own part, we felt as if we entered a new world when we gazed upon hills, and their long-furrowed escarpments, of this calcareous snow-drift. Our acquaintance with the mineral had hitherto been limited to the fragments with which we were wont to trace the lines of our schoolboy pastimes. We got no deeper into its mysteries when, on a higher scale of action, we saw it delineate the diagram, or run over the fluxional problem on the black-board in academy and college-hall. But here! and half an island is covered with these stores of knowledge and of industry. Nine or ten counties on a stretch, from Dorset to Flamborough Head, and from Bridport to Deal, are covered over, and for hundreds of feet in depth, with the milk-white earth; and, whichever way you turn and bend toward the Capital, there are ample opportunities for the study of this curious page of geological history. The chalk beds are not composed of one uniform compact mass of the useful mineral itself, which consists of nearly pure carbonate of lime, of soft earthy texture. Geologically considered, the cretaceous system comprises a series of green and ferruginous sands, clays, marls, gray and white limestones; and these again are arranged under three leading groups—chalk, gault, and green sand. The _chalk_—properly so called—is subdivided into the upper and lower,—containing in the upper numerous veins and nodules of flint, and varies in color through several intermediate hues, until, in its contact with trap, it assumes a deep red. The _gault_ is an argillaceous deposit of stiff, dark blue clays, highly calcareous, and effervesces freely with acids. The _green sand_ is a triple alternation of sands, cherty limestone, and friable sandstone, with beds, in some places of ocher and Fuller’s earth. The whole series may be estimated at nearly two thousand feet in thickness, formed in a deep sea basin, the materials floating in very still waters, and aggregated successively through the combined influence of mechanical, chemical, and organic agencies.