The occurrence of fluid cavities in quartz, chalcedony, sapphire, and other minerals, is due at times to cavernous structures formed during the growth of these minerals, when the crystalline substances, for some reason, instead of filling these up solid, will avoid the caverns and enclose the liquid of crystallization. In agate inclusions this is found with silicious content, possibly due to the fact that it is to an extent carbonic acid gas, or water containing salt or some other foreign substance. In agate chalcedony, whether in pebbles as minute as a pinhead, or in amygdules several feet across, the liquid is enclosed because the walls of the gas-pores in the rock, which are frequently almond-shaped, are gradually becoming smaller, or rather the walls thicken by the deposition of the silica forming agate, chalcedony, or any impenetrable layers, or else an impenetrable form of quartz; then again, frequently toward the centre or when the liquid forms less rapidly, or through some change, the quartz becomes crystalline, either colorless, smoky, or amethystine, and this is due to various inclusions. This gradual thickening of the walls means that the aperture into which the liquid penetrates becomes smaller and smaller until at last it is entirely sealed, so that it becomes enclosed in a kind of nature’s water-bottle, these being sometimes as large as in the chalcedony specimens from Uruguay; this is also the case with the hydrolites and the enhydros, when they can be shaken and the water rattles as in a bottle. An occasional small Redondo Beach, California, or Medford, Oregon pebble contains a moving bubble of air in liquid. Most wonderful specimens of rutilated quartz are the great, rich brown, possibly titanium-colored masses in the Morgan Collection at the American Museum of Natural History, that in the Vaux Collection at the Philadelphia Academy of Natural Sciences, and a smaller mass in the British Museum; these were all obtained near Middlesex, Vermont. The rutile is a rich transparent or translucent red, varying in thinness from that of an ordinary needle to that of a knitting-needle, and even to that of a thin lead-pencil. Wonderful specimens are also found in the Alps of St. Gotthard, in Madagascar, and in Alexander County, North Carolina, where they are found in quantity as minute crystals of a rich red or golden yellow.