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 jeweler. 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 steatite of St. 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 dessication, which commences the moment the rock is exposed to the air. The coloring matter of the emerald seems to be derived from the decomposition of the remains of animals who have lived in a bygone age, and whose remains are now found fossilized in the rock which forms the matrix of the gem. This rock in Granada is a black limestone, with white veins containing ammonites. Specimens of these rocks exhibiting fragments of emeralds _in situ_, and also ammonites, are to be seen in the mineralogical gallery of the Jardin des Plantes in Paris. Lewy believes that the beautiful tint of these gems is produced by an organic substance, which he considers to be a carburet of hydrogen, similar to that called chlorophyll, which constitutes the coloring matter of the leaves of plants; and he has shown that the emeralds of the darkest hue, which contain the greatest amount of organic matter, lose their color completely at a low red heat, and become opaque and white; while minerals and pastes which are well known to be colored by chromium, like the green garnets (the lime-chrome garnets) of Siberia, are unchanged in hue by the action of heat.