were so thin as to be translucent, and we caught the minutest details of their structure, the result of the long work of centuries (Salle de Draperies). Accordingly as the calcareous waters were or were not charged with salts of iron, bands alternately brown and white were deposited the whole length of the veil, simulating, in their regularity, the stripes of the richest tissues of the most complete factories. This hall, of all the caves I have visited, left the strongest impression of the 
Fig. 3.-A Passage in the Subterranean River Midroi. (From a photograph.) marvels to be met with in the bosom of the earth. Leaving this Hall of Draperies with regret, we continued our march, but were soon stopped, for the river went no farther on this side. We had traversed nearly five hundred and fifty yards in this resplendent cavern, and were now fifty yards above the mouth of the river. Before returning we took a second specimen of water for our studies. It came from a drip which would certainly in less than a year have caused the junction of a stalactite and a stalagmite, and never had we better observed the phenomenon of the union of calcareous concretions. A third specimen was taken from the dripping roof. As we have mentioned these microbic studies, we will also speak of the results we obtained.
As a general thing, the culture tubes in which the water from the dripping roof, stalactites in course of formation, and pot-holes in which the water had not been stirred for a long time was put, remained sterile—that is, did not contain microbes. But when we examined a drop of water from the vents, or those fine springs that escape from the fissures, or from the pot-holes or lakes of these subterranean rivers, colonies of microbes were developed; the calcareous filter is no longer sufficient, and while it stops the coarse impurities of the waters that fall on the plateau, it lets the
