The minerals already mentioned, quartz, feldspar, and mica, are the components of a large part of our granites. In the case of the red Scotch granite, another silicate, hornblende, replaces the mica. Various silicates of economic value are asbestos, a variety of hornblende, and augite, which are silicates of magnesium and iron or calcium; and talc, which is a silicate of magnesium containing water. A great number of gems are found among the silicates, including tourmaline, garnet, topaz, beryl, and chrysolite. THE DANGER FROM THE IMPORTATION OF ANIMALS. An abstract of J. S. Palmer's essay on "The Danger of Introducing Noxious Animals and Birds" appears in _Our Animal Friends_. There are several societies in this country for the express purpose of purchasing and importing European birds. One society in Cincinnati has contributed $9,000 to this object, and other cities have raised considerable sums. Our contemporary thinks it would be well that all such experiments should be made under the sanction of government experts of the Department or Agriculture. In addition to voluntary importations, it often happens that animals are unintentionally brought into the country, as trading-vessels have carried the European house mouse all over the globe, and the introduction of rabbits into Australia is perhaps the most striking example of the dangers of unconsidered importations. They were introduced for purposes of sport, and were liberated near Melbourne in 1864. Within twelve years they had spread over the country and become a veritable plague, and millions of dollars have been spent for bounties, poisons, and other methods of destruction. Thousands of miles of rabbit-proof fences have been built, and in 1887 no less than 19,182,539 rabbits were destroyed in New South Wales alone, and the rabbits seem to be on the increase. The little Indian mongoose was imported into Jamaica to cope with a plague of rats and proved most effective, but after it had destroyed the rats it turned its attention to the domestic animals and poultry, so that the islanders would now be glad if they could get rid of the pests. Such are a few examples of the danger of disturbing nature's balance. THE AMERICAN BISON. A remarkable article recently appeared in the _Scientific American_, written by Prof. Chas. F. Holder, entitled, "A Crime of a Century," in which is described the extermination, the wiping out of the American bison. "In 1870, and later," said an army officer, "the plains were alive with bison, and in crossing at places I had difficulty in avoiding them, so vast were the herds. If anyone had told me then that in twenty or thirty years they would have become almost entirely extinct I should have regarded the statement as that of an insane person."