Page:Popular Science Monthly Volume 46.djvu/149

Rh period," and other turtlebacks not so explainable, "and seeming to betoken a period of unknown direction before the working of the quarries." In Durham Cave, Stroudsburg, Pa., instead of a pre-Indian cave man, a red man was found, "as the contemporary, it seemed, of the peccary and giant chinchilla." In the chalk gorges of southern Texas, apparently promising indications gave only tokens of modern surface loam, which had fallen and mingled with ancient underplaced chalk. The cave at Lookout Mountain was explored to the bottom. Teeth of the tapir close to the layer of occupancy by man, added, however, a new species to the list of extinct North American mammals thus far observed in like association with human remains. The Nicajack Cave, in Marion County, Tenn., likewise failed to yield any earlier than neolithic remains.

Kinds of Ivory.—Four principal kinds of ivory are known in the market: that of Guinea, the Gaboon, or Angola, which is a little greenish, so that it is sometimes called green ivory, and which whitens with age; Cape ivory, which is of a dull, light, somewhat yellowish color; Indian or Siamese ivory, very rare, and white, with a tinge of rose color; and the fossil ivory of Siberia, remains of the mammoths of the olden time. Of these, the West African ivory is most highly prized, being finer and more transparent than the others. It is pretended that experts, when they see a well-preserved tusk, can tell whether the animal that wore it came from East or West Africa, or north or south of the equator. The farther north the animal's habitat, and the more elevated and dry the situation, the more the ivory is coarse and inferior. The principal market for ivory is at Liverpool, and nearly one third of the stock imported there is used in the Sheffield cutleries. Another considerable market is at Antwerp. The annual exports of ivory from Africa represent the product of sixty thousand elephants, and this means a rapid reduction of the elephantine population of the continent. Various artificial ivories, or imitations, are manufactured to supply the increasing demand. There are vegetable ivory—tagua seed from Peru, or wood injected with chloride of lime; sheep bone, macerated with the wastes of white skins; paper pulp with gelatin, celluloid, and caoutchouc; a preparation of potatoes; and a substance obtained by treating milk with certain reagents. The expediency has been suggested of establishing elephant farms, to form a more certain source of supply than hunting wild elephants is destined to become. Ostrich farming has proved practicable; why not elephant farming too?

Migration of Birds.—On the solution of the problem of the migration of birds. Canon Tristram said in the British Association, much less aid has been contributed by the observations of field naturalists than might reasonably have been expected. The observable facts may be classified as to their bearing on the whither, when, and how of migration, and after this we may possibly arrive at a true answer to the Why? Observation has sufficiently answered the first question. Whither? There are scarcely any feathered denizens of earth or sea to the summer and winter ranges of which we can not now point. Of almost all the birds of the holo-arctic fauna we have ascertained the breeding places and the winter resorts. Now that the knot and the sanderling have been successfully pursued even to Grinnell Land, there remains but the curlew sandpiper of all the known European birds whose breeding ground is a virgin soil, to be trodden, let us hope, in a successful exploration by Nansen, on one side or other of the north pole. Equally clearly ascertained are the winter quarters of all the migrants. The most casual observer can not fail to notice in any part of Africa, north or south, west coast or interior, the myriads of familiar species which winter there. We have arrived at a fair knowledge of the When? of migration. Of the How? we have ascertained a little, but very little. The lines of migration vary widely in different species and in different longitudes. All courses of rivers of importance form minor routes. Consideration of all lines of migration might serve to explain the fact of North American stragglers, the waifs and strays which have fallen in with great flights of the regular migrants, and been more frequently shot on the east coast of England and Scotland than on the west coast or in Ireland. They have not crossed the Atlantic, but have come from