A few miles west of the Rapids of the Canadian, a thin stratum of compact limestone, of the common blue variety, and abounding in organized remains, overlays the argillaceous sandstone of the coal formation. This limestone becomes more abundant towards the south, and is the prevailing rock on that part of Red river, near the confluence of the Kiamesha.[84] At Cape Girardeau, in the country a few miles in the rear of Herculaneum and St. Genevieve, and in many places throughout the district of the lead-mines, there is a coarse crystalline limestone, of a light gray colour, which is usually the lowest rock exposed in those places. It is very indistinctly stratified, and has in many respects a considerable resemblance to the more crystalline varieties of primitive limestone: for such it appears to have been mistaken by Mr. Schoolcraft, who, in his work on the lead-mines, asserts that the "mineral soil at Mine a Burton, and the numerous mines in its vicinity, reposes on primitive limestone," page 108. Afterwards, at page 119., speaking of this same primitive limestone, he says, "On going deeper, the rock again graduated into a compact limestone, very hard, and of a bluish gray colour, in which were frequently found small cavities studded over with minute pyramids of limpid quartz." And again, at the page first referred to, he informs us, "The primitive limestone passes into transition, and secondary, in various places on the banks of the Mississippi, between Cape Girardeau, and Saint Louis." We adduce these statements as confirming our own observations of the alternation of the _crystalline_ or _sparry_ limestone, with the compact blue variety; but as we have examined with great care several of the places mentioned by Mr. Schoolcraft, and many others apparently similar, we are disposed to think he has mistaken the character of the rock. We have never met with any {302} limestone about the lead-mines which did not contain organized remains; and the white crystalline variety abounds particularly in casts of encrinites, though these are not always manifest without careful examination. This limestone, though rather indistinctly stratified, is marked by horizontal seams, distant one or two feet, and sometimes more, from each other. Its exposed surface becomes somewhat bleached and rough with small prominences, in which we may often distinctly trace the forms of animal remains. The recent fracture is uneven, distinctly crystalline, and much like that of many moderately fine-grained granites. Careful examination shows that in many instances the most minute particles visible under a lens, have assumed the rhombic form so common to the carbonate of lime. These crystalline particles vary greatly in size, and are sometimes half an inch across. In the interior of the casts of animal remains, they are sometimes less distinct than in parts of the rock where no such remains are discovered.