M. Lewy visited the mines at Muzo in Granada, and from the results of his analyses, together with the fact of finding emeralds in conjunction with the presence of fossil shells in the limestone in which they occur, he arrived at the conclusion that they have been formed in the wet way,--deposited from a chemical solution. He also found that when extracted they are so soft and fragile that the largest and finest fragments can be reduced to powder by merely rubbing them between the fingers, and the crystals often crack and fall to pieces after being removed from the mine, apparently from loss of water. Consequently, when the emeralds are first extracted they are laid aside carefully for a few days until the water is evaporated. This statement relative to the softness of the gem and its subsequent hardening has been met with a shout of derision from some of the gem-seekers,--none louder than that of Barbot, the retired jeweller. Barbot seems to forget that the rock of which his own house in Paris is constructed undergoes the same change after being removed from the deep quarries in the catacombs under the city. This phenomenon is observed with many rocks. Flints acquire additional toughness by the evaporation of water contained in them. The yellow gneiss of Ceylon is soft when quarried, but hardens on exposure to the atmosphere. The Egyptian verde antique marble, which was named after Augustus and Tiberias, was easily quarried with steel implements, but quickly hardened on exposure to the external air. The mosaic plates of this mineral which are inlaid in the decorative work of the Tuscan Gothic buildings are yet quite hard. The steatite of Saint Anthony’s Falls grows harder on exposure, and other minerals, when quarried from considerable depths, become firmer on exposure to the action of the air. Observations of this kind led Kuhlman to investigate the cause; and he believes that the hardening of rocks is not owing solely to the evaporation of quarry-water, but that it depends upon the tendency which all earthy matters possess to undergo a spontaneous crystallization by slow desiccation, which commences the moment the rock is exposed to the air.