Agate
a mineral classed by Dana as one of the cryptocrystalline varieties of quartz, some of the other minerals falling ing under the same category being Water Fishes of Europe"; and "Con- tributions to the Natural History of the United States." Other important works are "Studies on the Glaciers," "The Glacial System," and "Researches on Fos- sil Fishes." He died at Cambridge, Mass., and jasper.
In Archæology. - The Danish and Swedish antiquaries and naturalists, MM. life. The precise time of human exsen, Worsaae, and others, have divided the period during which man has existed on the earth into three the age of stone, this into two-the paleolithic, or older, the age of bronze, and the age of iron. and the neolithic, or newer, stone period.
During the first-mentioned of these he is supposed to have had only stone for weapons, etc. Sir John Lubbock divides At the commencement of the age of gan gradually to be superseded by the bronze that composite metal became known, and began to be manufactured into weapons and other instruments; while, when the age of iron came in, bronze be- AGE last-mentioned metal. (Lyell's "The Antiquity of Man"; Lubbock's "Prehistoric Times.") In Law, the time of competence to do certain acts. In the United States, both males and females are of full age at 21. The age at which minors may be punished or may marry varies in the several States.
Age of Animals. The duration of life in animals is generally between seven and eight times the period which elapses from birth till they become adult; but this rule, besides being vague and indefinite, is quite useless in practice, because it affords no scale of graduation which would enable us to ascertain the pr precise age of individuals.
Age of Plants. Plants, like animals, are subject to the laws of mortality, and, in many cases, have the period of their existence determined by nature with as much exactness as that of an insect. It is principally to annual and biennial plants that a precise period of duration is fixed. The remainder of the more perfect part of the vegetable kingdom, whether herbaceous, or shrubby, or arborescent, consist of plants which may be classed under two principal modes of growth. One of these modes is to increase, when young, in diameter, rather than in length until a certain magnitude is obtained, and then to shoot up a stem, the diameter of which is never materially altered. The addition of new matter to a trunk of this kind takes place by the insinuation of longitudinal fibers into the inside of the wood near the center; on which account such trees are called endogenous, or monocotyledons. The other mode is, from the beginning, to increase simultaneously in length and diameter, but principally in length. The addition of new matter to a trunk of this kind takes place by the insinuation of longitudinal fibers into a space beneath the bark, and on the outside of the wood, near the circumference; on which account such trees are called exogenous, or dicotyledons. The way by which the age of exogenou trees may be computed is by cutting out a portion of their circumference, and counting the number of concentric rings that are visible; the woody cylinder of one year being divided from the succeeding one by a denser substance, which marks distinctly the line of separation of the two years. In consequence of the extreme inequality in thickness of the annual layers of wood on opposite sides of a stem, a person judging of the whole age of a tree by the examination of the layers of the stunted side only would commit errors to the amount of 60 per cent., and more.
AGINCOURT AGEN (ä-zhon'), a town of France, capital of the department of Lot-et-Garonne, on the right bank of the Garonne, on the railway from Bordeaux to Toulouse. Its situation, though rather unhealthy, makes it the entrepôt of the commerce between Bordeaux and Toulouse. The town is very ancient, seat of a bishop, and possesses a cathedral dating back to the 6th century. Pop. about 25,000.