Every part of this formation has more or less the appearance of a mineral country; and it is already known as the locality of ores of lead, iron, and zinc, of crystallized quartz, of opal, heavy spar, crystallized pyrites, and of very perfect fossil madrepores. In one place (near the head of Hurricane Island) this spar forms a very large and compact vein, dipping under the bed of the Ohio. Where the rock has been explored, it is found in connection with sulphuret of lead, but it has been mostly procured, because most easy of access, in the alluvial soil. I went out about half a mile west of the Ohio, where a new locality has been opened, and, in removing about five or six solid feet of earth, procured as many specimens as filled a box of fourteen inches square. None of these were more than two feet below the surface. One of these specimens is an irregular octahedral crystal, eight inches in diameter. The color of these masses is various shades of blue, violet, or red, sometimes perfectly white or yellow; and the form most commonly assumed is a cube, sometimes truncated at two or more angles, or variously clustered. The external lustre of the crystals, raised from alluvial soil, is feeble, but quite brilliant when taken from veins and cavities in the rock. These spars from the alluvion do not appear to exist as rock debris, or fragments worn off from other formations, but as original deposits. There are no marks of attrition. They appear as much in place as the limestone rocks below. It should also be recollected that this mineral tract is terminated by one of the greatest and most valuable salt formations in the western country--that of the Illinois Saline. _Septaria: Ludus Helmontii._--This variety of calcareous marl is found, in orbicular or flattened masses, along the eastern shores of Lake Michigan, between the rivers St. Joseph's and Kalemazo. Its original situation appears to be the beds of marly clay which form the banks of Lake Michigan at these places, from which these masses have been disengaged by the waves, and left promiscuously among the washed and eroded debris of the shore. These masses are penetrated by numerous seams and lines of calcareous spar, sometimes radiating star-like, or intersecting each other irregularly. Occasionally, these seams are filled with sulphuret of zinc, and in these cases the spar, if any be present, is rose-colored. d. _Aluminous Minerals._ 1. ARGILLACEOUS SLATE. 1. _Argillite_, or _Common Argillaceous Slate_.--Along the banks of the River St. Louis, at the Grand Portage, &c. It occurs in a vertical position, embracing veins, or subordinate beds, of grauwakke, milky quartz, chlorite slate, and silicious slate, &c. It is bounded on one side by red sandstone, and on the other by an extensive tract of diluvial soil.