Page:Popular Science Monthly Volume 33.djvu/659

Rh, or the wood, without losing its texture, has been completely replaced by peroxide of iron and quartz.

Nothing is clearer than the intervention of subterranean waters in the origin of many masses of calamine, in which zinc occurs in the condition of a carbonate and a hydrated silicate, at Veielle-Montagne, for example, not far from Aix-la-Chapelle. The mining works have enabled us to recognize and follow the channels of the generating springs in all their details. The calcareous walls between which they made their way have been attacked, and, as we have just seen to have been done with peroxide of iron, zinc mineral has been gradually substituted for carbonate of lime. The springs that held the mineral in solution issued from faults, and insinuated themselves into the permeable strata, flowing upon the surface of the impermeable beds. Vestiges of fossil shells, sometimes including the minerals of zinc and lead, in Westphalia, for example, likewise attest the substitution of metallic combinations for limestone. The lead and silver mines of Laurium, one of the principal sources of Athenian wealth, which figured in the budget of that state from the year 520 have revealed, perhaps still more evidently, in their vast excavations, the same processes of Nature.

Similar instances occur in many other countries. We cite in France the various calamine beds on the circumference of the central plateau; and, in the United States, in the Rocky Mountains, the important beds that have given rise to the towns of Eureka and Leadville. Notwithstanding local differences, all these masses of calamine present striking analogies, quite independent of the age of the beds in which they are spread. The metallic sheets are always in the same relation of situation with respect to the permeability and chemical nature of the rocks as they would be to-day, if the metalliferous waters were continuing to flow. It is thus made possible to determine exactly all the ruling conditions of these ancient zinc-bearing streams.

Phosphorus is most usually found in the crust of the earth in the state of phosphate of lime or phosphorite. It is extracted for the wants of agriculture from certain layers of the stratified beds and in the cretaceous formation, particularly in the beds called the gault, the same as those from which flows the water of the well of Grenelle. This mineral has been worked very actively since 1855 in several of the departments of France, in England, Bavaria, North Germany, Russia, Spain, and Poland. It also exists in remarkable quantities in the Jurassic. It often, in these beds, contains animal forms, as of bones, indicating that it has passed through life. But when it appears in eruptive rocks and metalliferous veins, its origin is wholly independent of the action of organized beings. Like the metals, the phosphorus now