The metalliferous, red, marly clay, is, in fine, the most interesting geological problem connected with the mines, and is calculated to show us how little we know of the true eras of the diluvial deposits. After every examination which we have been able to make, we are decidedly of the opinion that this formation belongs to the diluvial, and not to the alluvial era. It seems, indeed, to assert a claim to be considered, among the western strata, as immediately succeeding the secondary. It lies directly next to, and upon, the limestone rock. We have witnessed the progress of an excavation on the public square of Potosi, in which the soil was removed down to the rock, and a clean area of its surface was exposed. There was no other stratum below it, and between the clay and rock. And such we believe to be its general position. The radiated quartz and pebble drift is above it, and, consequently, constitutes a subsequent deposit. And hence it is that the numerous fragmentary masses of the former, called mineral blossom, are no sure indications of the subterraneous presence of ore. The gravel-ore and mixed diluvial gravel is likewise a newer deposit, coinciding with the era of the primitive and secondary boulders. No large primitive boulders, however, exist in the mine district, if we except the angular fragments of granite, south of St. Michael, which are, indeed, just without the lead-yielding area. Pebbles of common quartz, granite, and greenstone, are found in the surface soil, and are also to be observed, in accumulated masses, in the beds of brooks. Occasionally an orbicular mass of these rocks, of the size of a melon, is observed. It is evident, from these appearances, that no formations of the primitive exist, towards the sources of the Mississippi, for a great distance, as it is from this direction that diluvial action appears to have been propagated. This clay soil is free from boulders, and is of a homogeneous texture. It partakes, in its qualities, so largely of marl, as to operate as a manure, on being thrown out of the pits, and, after a few years, is covered with a very rank growth of trees, vines, &c. This is a characteristic trait of the locality of abandoned diggings.

The following is a catalogue of the mines. It comprises those of most note, which are now worked, or have been at some former period.

1. Mine à Burton.24. Tapley's Diggings.
2. Mine à Robino.25. Lambert's Diggings.
3. Mine à Martin.26. Old Mines.
4. New Diggings.27. Mine Shibboleth.
5. Citadel Diggings.28. Elliot's Mines.
6. Perry's Diggings.29. Belle Fontaine.
7. Hawkins's Mine.30. Cannon's Mines.
8. Rosebury's Mine.31. Little Diggings.
9. Austin's Shaft.32. Becquet's Diggings.
10. Jones's Shaft.33. Mine Liberty.
11. Rocky Diggings, (Prairie de Roche).34. Renault's Mines.
12. Gravelly Diggings.35. Miller's Mine.
13. Brushy-run Diggings.36. Mine Silvers.
14. Stricklin's Diggings.37. Fourche à Courtois.
15. Bibb's Diggings.38. Pratt's Mine, Big river.
16. Tebault's Diggings, (Pinery).39. Lebaum's Mine, Richwoods.
17. Mine Astraddle.40. Mine à Joe, Flat river.
18. Masson's Diggings, or Partney's.41. Bryan's Mines, Hazel run.
19. J. Scott's Diggings.42. Dogget's Mine. Hazel run.
20. T. Scott's Diggings.43. Mine La Motte, St. Michael.
21. Micheaux's Diggings.44. Gray's Mine, Big river.
22. Henry's Diggings.45. M'Kain's Mine, Dry creek.
23. Moreau's Diggings.

The most noted mines are Mine à Burton, New Diggings, Shibboleth, Richwoods, Old Mines, and the numerous mines on the waters of the Mineral Fork of Grand river. Mine à La Motte, Mine à Joe, and Bryan's Mines, are east and south of the principal group of mines in Washington county, and at a considerable distance from them. A few general remarks may be applied to all these mines.

The mines possess one general character, although there are some peculiarities which I shall hereafter mention. The ore is found in detached pieces and solid masses, in beds, in red clay, accompanied by sulphate of barytes, calcareous spar, blende, iron pyrites, and quartz. The ore is of that kind called, by mineralogists, lead-glance, or galena, and is the sulphuret of lead, of chemistry. As it is dug up or quarried from the adhering spar, it presents a very rich appearance. It has a broad, glittering grain, of a lead-gray colour, which passes into a bluish shade. The ore is easily broken by the blow of a hammer, and may be pounded to a fine powder, still preserving its glittering appearance. In breaking it, it always separates in cubes. Sometimes detached lumps of four or five pounds weight, of a cubical form, are found imbedded in the clay. Its primitive figure of crystallization is particularly observable after the ore has been desulphurated by heat, which, at the same time, increases its splendor, and renders the lines of intersection between the facets more plainly discoverable.

The clay, or red earth, in which the ore is found, appears to partake largely of marl; and a difference of quality is to be observed at the different mines. It all, however, operates more or less as a stimulant to vegetation, on being thrown out of the pits. Mixed with the clay are innumerable pieces of radiated quartz, very beautiful in appearance. This forms the first stratum, and is about fourteen inches in depth; then succeeds a stratum of red clay, four or five feet thick, and sparingly mixed with substances of the same kind; after this, a layer of gravel and rounded pebbles, of a silicious character, ensues; these are about a foot in depth, and lead-ore, in small detached lumps, is then found. This is of the description called gravel-ore, and no spars are found accompanying it. The greatest proportion of lead-ore is, however, found imbedded in marly clay, accompanied by the sulphate of barytes, and resting on limestone rock. The rock is struck at a depth of from fifteen to twenty feet, and is a metalliferous limestone, of a semi-crystalline structure, lying in horizontal beds. It is traversed by veins of lead-ore. Sometimes these expand in the shape of caves, where masses of galena occur.

The most valuable substance accompanying the lead-ore, is an ore of zinc, which is found at several of the mines. Another substance, found with the ore in considerable quantities, is the sulphate of barytes. This is sometimes in immediate connection with the ore, but more frequently in contiguous masses, in the clay.

The sulphate of barytes, called tiff by the lead-diggers here, is the same substance called cawk by English miners. It is very white, opaque, and very heavy, and may be considered as the proper matrix of the lead-ore.

There are also found considerable quantities of calcareous spar, particularly in the caves and veins in rock. This substance is often observed in large orbicular or irregular masses, which have the appearance of external attrition. On breaking them, they fall into rhombs, which are very transparent and glittering; in color, they are either white, or honey-yellow.

Pyrites are common at the mines, sometimes crystallized in regular cubes of a beautiful brass-yellow color, and, at others, found in tabular masses, or mixed with blende, sulphate of barytes, or calcareous spar. Quartz is found throughout the whole mine district, both on the surface of the ground, and at all depths below. It is generally in the form of tabular pieces, whose surfaces are thickly studded over with small pyramids of transparent rock-crystal, and present an appearance of the utmost beauty and splendor, looking like so many diamonds set over the surface of white stone. These crystals are frequently grouped in the form of a hemisphere, circular, or oviform, solitary or in clusters, forming the different varieties of mamillary and radiated quartz, and, when met with in their pristine beauty, present a very rich and brilliant appearance. It has acquired the popular name of blossom of lead, or mineral blossom, a term perfectly significant of its supposed affinity.