went on in a single class of animals. There must have been corresponding rates of extinction in the ease of birds, fishes, and insects.
The rapid summary we have given of the successive changes and revolutions in the earth's history, and the fact that they are accompanied or followed by the process of the extinction of the unadapted, and their replacement by the more specialized and better adapted, show that there is between these two sets of phenomena a relation of cause and effect. The subject is further illustrated by the extinction of life in South America.
The Andean plateau during the Quaternary period was paroxysmally elevated into the air some 12,000 feet. Packard calls attention to the possible results of such an enormous upheaval on the plants and animals of this region. Before and at the time this movement began, when the land was 12,000 feet lower than now, the Atlantic trade winds which now cross Brazil, impinge upon the Andes, and drop their moisture on the eastern slopes alone, then favored as well the western slopes and Pacific coast. The tropical flora and fauna now confined to the neighborhood of Guayaquil on the coast of Peru then probably spread over Bolivia, Ecuador, Peru, and Chile to Patagonia. At Riobamba, altitude 9200 feet, the climate and vegetation are temperate; here occur bones of the mastodon, horse, deer, and llama—animals which may have lived in a temperate climate. But was not their extinction, and that of the colossal sloths, armadillos, and other animals of the pampas largely due to a change of climate resulting from the elevation of the Andean plateau? As the land gradually rose, the atmosphere would become more rarefied and insupportable to tropical life; the animals and plants would either seek lower levels or undergo extinction, or in certain eases become modified into species suited to a temperate climate. As the plateau rose still higher, the air would become too cold and rarefied for even the mastodon and horse. Gradually an alpine zone became established, and finally the higher peaks of the Andes, at an elevation of 15,000 feet, became mantled with perennial snow, and on Chimborazo glaciers established themselves. We thus see how, within Quaternary times, temperate and alpine zones became established over the vast Andean plateau, originally, perhaps at the end of the Pliocene, a plateau of the third order, clothed with vast forests like those of Brazil and Venezuela.
Another, but more local cause of extinction, is seen in Great Salt Lake, Utah. Formerly this was a vast fresh-water lake, abounding in fish, insects, mollusks, and plants. When it was by elevation of the lake-basin transformed into a brine-pool, all life was extinguished, except a shrimp, a single species of fly, and an alga. So with deserts; when they are formed life is reduced to a relatively small proportion.
That there is a limit to the age of species as well as to individuals almost goes without saying. As there is in each individual a youth, manhood, and old age, so species and orders rise, culminate, and decline, and nations have risen, reached a maximum of development, and then decayed. The causes, however complex, are, in the case of plants and animals, apparently physical; they are general and pervasive in their effects, and have been in operation since life began; there have been critical periods in paleontological as well as geological history, and periods of rapid and widespread extinction as well as a continual, progressive dying-out of isolated species. Such extinction was, so to speak, a biological necessity, for otherwise there would have been no progress, no evolution of higher types.
Bibliography. Darwin, Origin of Species (London, 6th ed., 1882); Searles V. Wood, “On the Form and Distribution of the Land Tracts during the Secondary and Tertiary Periods, respectively, and on the Effects upon Animal Life which great changes in geographical configuration have probably produced,” in Philosophical Magazine, xxiii., p. 161 (Edinburgh, 1862); A. S. Packard, “Geological Extinction and some of its apparent causes,” in American Naturalist, xx. 29-40 (Philadelphia, January, 1886); “A Half-Century of Evolution, with special reference to the effects of Geological Changes on Animal Life,” in Proceedings of the American Association for the Advancement of Science (Boston, 1898); J. B. Woodworth, “Base Levelling and Organic Evolution,” American Geologist, xiv. (October, 1894).
EXTORTION (ML. extortio, Lat. extorsio, from extorquere, to extort, from ex, out + torquere, to twist), in its widest sense, any form of taking or obtaining anything from another by means of illegal compulsion or oppressive exaction. As a technical term of the common law it has been judicially defined as the “crime committed by an officer of the law, who under color of his office unlawfully and corruptly takes any money or thing of value that is not due to him, or more than is due, or before it is due.” It is by the common law a misdemeanor punishable by fine and imprisonment, and subjecting the offender to removal from office. In most of the United States the term has received statutory definition. For example, in New York it is defined as “the obtaining of property from another. with his consent, induced by a wrongful use of force or fear, or under cover of official right.” (New York Penal Code, § 552.) See Encyclopædia of Pleading and Practice, viii. (Northport, 1897).
EXTRACT (ML. extractus, extract, from Lat. extractus, p.p. of extrahere, to draw out, from ex, out + trahere, to draw). In a medical or pharmaceutical sense, any vegetable preparation obtained by treating a plant with a solvent and evaporating the solution to about the consistency of honey; or by expressing the juice of the plant and evaporating—forming respectively liquid and solid extracts. Extracts contain only those vegetable principles that are either held in solution in the juices of the plants themselves, or are soluble in the liquid employed in extracting them, and at the same time are not so volatile as to be lost during evaporation. Now, as many extractive matters are more or less volatile, it makes a great difference whether the operation is conducted at a low or at a high temperature. Extracts are called watery or aqueous, alcoholic, or ethereal, according to the menstruum employed. Different plants of course afford different extracts, some being of the nature of bitters, others being used as pigments, tanning substances, etc. Extracts are liable to great uncertainty in point of strength and composition, and require to be prepared with great care.
