M. Desnoyers points out the close analogy between caverns and mineral veins, and infers that both are due to the same causes. This, undoubtedly, exists in that class of veins which are known to miners as “pipe” and “flat veins;” and there is clear proof, in the majority of cases, that the cavities in which the minerals occur have been formed by the action of running water, and have subsequently been more or less filled with their mineral contents; and these have been deposited on the sides of the cavity by the same “incretionary[35]” action, as that by which dripstone is now being formed in the present caves from the solution of carbonate of lime. Such veins present every conceivable form of irregularity, and frequently contain silt, sand, and gravel, which have been left behind by their streams, and their history is identical with that of the caverns. It is not so, however, with the second class of veins, the “rake,” “right running,” and “cross courses,” as the miners term them, or those which occupy lines of fault. The fissures which contain the ore are proved very frequently, by their scratched and grooved sides, and polished surfaces or slicken-sides, to have been the result of subterranean movements by which the rock has been broken by mechanical force. They have been subsequently modified, in various ways, by the passage of water, and filled with minerals, in the same manner as the preceding class. With this exception they present no analogy to the caverns, with which they contrast strongly in their rectilinear direction, as well as in their purely mechanical origin. _The various Ages of Caves._