OCR Text |
Show 82 GLOSBARV. which distinguish them from two other great series of strata,the secondary and primary, which lie beneath them. See Tables, p. 61, &c. TESTACEA. Molluscous animals, having a shelly covering. Etym., testa, a shell, such as snails, whelks, oysters, &c. THIN ouT. When a stratum, in the course of its prolongation in any direction, becomes gradually less in thickness, the two surfaces approach nearer and nearer; and when at last they meet, the stratum is said to thin out, or disappear. TRACHYTE. A variety of lava essentially composed of glassy felspar, and frequently having detached crystals of felspar in the base or body of the stone, giving it the structure of porphyry. It sometimes contains hornblende and augite; and when these last predominate, the trachyte passes into the varieties of trap called greenstone, basalt, dolorite, &c. The term is derived from rpaKv~, trachus, rough, because the rock has a peculiar rough feel. TnAP and TRAPPEAN RocKs. Volcanic rocks composed of felspar, augite, and hornblende. The various proportions and state of aggregation of these simple minerals, and differences in external forms, give rise to varieties, which have received distinct appellations, such as basalt, amygdaloid, dolorite, greenstone, and others. The term is derived from trappa, a Swedish word for stair, because in Sweden the rocks of this class often occur in large tabular masses, rising one above another, lil<e the steps of a staircase. For further explanation, see vol. iii. p. 359. TnAV.I!!RTIN. A limestone, usually hard and semi-crystalline, deposited from the water of springs holding lime in solution. The word is Italian, and a corruption of the term Tiburtinu.~, the stone being formed in great quantity by the river Anio, at Tibur, near Rome, and hence it was called by the ancients Lapis Tiburtinus. TnoPm, of Insects. Organs which form the mouth, consisting of an upper and under lip, and comprising the parts called mandibles, maxillre, and palpi. TurF, or TuFo. An Italian name for a variety of volcanic rock, of an earthy texture, seldom very compact, and composed of an agglutination of fragments of scorire and loose matter ejected from a volcano. TuFACEous. A rock with the texture of tuff or tufo, which see. TuRBINATED. Shells which have a spiral or screw-form structure. Etym., turbinatus, made like a top. GtOSSAln~. 83 VEINS, Mineral. Cracks in rocks filled u b . from the rock, which may eithe b P 1 Y substances d1fferent . r e eart JY or met 11' V . are sometimes many yarcls wide . d th . a tc. ems into innumerable smaller parts 0 'ftan eyl ramify or branch off . . • en as s ender as th d l'k the vems m an animal ' and hence th e1. r name rea s, 1 e VERTEBRATED ANIMALS. A great divi · f h. . . . I a· ll SlOn o t e ammal lnngd me u mg a those which are furnish d 'th b om, mammalia, birds, reptiles and fishes e Twl1 a ack-bone, as the ' · 1e separate J. oi t f th back-bone are called vertebrce from the 1 t' b n 8 0 e V A . ' a In ver verto to turn ESICLE. small cucular inclosed space l'k 1. 1 ' · Et d . · · ' 1 e a 1tt e bladder ym., 1mmubve of vesica, Latin for a bladder . VoLCANIC BoMBs. Volcanos throw out sometimes d. t h d f I d 1 1 · e ac e masses o mete ava, w nch, as they fall, assume rounded forms (like bomb-shells), and are often elonga•t ecl 1'nto a pearsh ape. Voi.CANIC Focr. Th.e subterranean centres of a c· t·1 on m· vo 1c anos where the heat IS supposed to be in the h.I g 11 es t de gree of' energy. ZEOLITE. A f~mily of simple minerals, including stilbite, mesotype, ~nalCime, and some others, usually found in the trap or vo~camc rocks. Some of the most common varieties swell or b01l up when exposed to the blow-pipe, and hence the name of ~£w, zeo, to froth, and 'AtBo~, lithos, stone. ZooPHYTES. Corals, sponges, and other aquatic animals allied to them, so called because, while they are the habitation of animals they are fixed to the ground, and have the forms of plants: Etym., ~wov, zoon, animal, and q>vroY, phyton, plant. /2 |