TEU 



TEX 



paper consists of letter-paper dipped 

 several times into a filtered solution of 

 litmus, and dried after each immersion, 

 until it is of a deep purple colour. 



TESTA. Literally, a shell ; and, hence, 

 applied by botanists to the integuments 

 of the seed. By Mirbel, these integu- 

 ments are called lorica, by Richard peri- 

 sperm and episperm, and by De CandoUe 

 spermoderm. It appears to coilsist of two 

 coats, and, in succulent seeds, of an 

 intervening substance called sarco- 

 derm. 



TESTA'CEA {testa, a shell). Mol- 

 luscous animals, having a shelly cover- 

 ing, as the oyster. 



TESTUDl'NIDiE {testudo, a tortoise). 

 Land-tortoises ; a family of Chelonian 

 reptiles, distinguished by their highly 

 arched carapace, and short clubby feet. 



TETRABRANCHIA'TA (rexpaf, four, 

 flpdyxia, gills). An order of Cepha- 

 lopods, represented in modern times by 

 the Pearly Nautilus, in which there are 

 four branchial organs, two on each side. 

 See Dibranchiata. 



TE'TRACHORD (rexpaf, four, xop^n, 

 a chord). The Greek name for any part 

 of the scale of music consisting of four 

 notes, the higliest of which is a perfect 

 fourth to the lowest. 



TETRADYNA'MIA (rerpa?, four, 

 bvvaixi^, power). The fifteenth class of 

 Linnaeus's system of plants, characterized 

 by the presence of six stamens, of which 

 four are long, two short, as in Stock. 



TE'TRAGOX (reTpa?, four, -iuivia, an 

 angle), A figure with four angles, 

 usually applied jonly to the square. 



TETRAHE'DRON (rexpcW, four, 'e6pa, 

 a seat). A geometrical solid contained by 

 four equal and equilateral triangles. 



TETRA'MERA (xexpci?, four, nepo^, 

 a part). A section o' Coleopterous in- 

 sects, in which all the tarsi have four 

 distinct joints, the fifth being very mi- 

 nute, and concealed in the others. La- 

 treille. 



TETRA'NDRTA (xexp.ic, four, itv^P, 

 mile). The fourth class of plants in 

 Linnaeus's system, characterized by the 

 presence of four stamens of equal length. 

 See Didijnamia. 



TETRAO'NID.^ {tetrao, the grouse). 

 The Grouse family of the Rasores, or 

 Scratching Birds, characterized by their 

 very short hind toe and very short tail. 

 They differ as little from the partridges 

 as these from the pheasants. They vary 

 much in size. 

 TEU'THIDiE {teuthis, a calamary). A 

 334 



family of Cephalopods, of which the 

 loligo vulgaris, or teuthis, is the type. 



TEXTURE OF ROCKS. By texture 

 is meant the mode of aggregation of the 

 mineral substances of which rocks are 

 composed, and it relates to the arrange- 

 ment of their parts viewed on a smaller 

 scale than that of their structure. In 

 this respect rocks may be simple or com- 

 pound, that IS, composed of a single mine- 

 ral species, or of several species. Com- 

 pound rocks are said to be fragmentary, 

 when their particles or fragments are 

 united by a cement; aggregated, when 

 their particles cohere without the inter- 

 vention of a cement. 



1. The texture of simple rocks is said 

 to be, 1, compact, when the particles or 

 crystals are so minute as not to be dis- 

 tinguished by the naked eye, as in some 

 kinds of felspar and limestone ; 2, earthy, 

 when the particles are minute, and hav- 

 ing little cohesion, readily crumble, as in 

 some kinds of chalk ; 3, granular, when 

 the particles or crystals are distinguish- 

 able, and of arounded form, as in oolite ; 4, 

 crystalline, when the particles are readily 

 distinguishable, confusedly aggregated, 

 and present the appearance of imperfect 

 crystals, as in primary limestone ; 

 5, scaly, when the particles are disposed 

 in the form of small scales, as in some 

 varieties of clay-slate ; 6, lamellar, when 

 the rock is composed of very thin la- 

 mellae, or plates, as in some kinds of 

 pitchstone; 7, laminar, when composed 

 of thin parallel laminae, or plates, as in 

 clay-slate; 8, fibrous, when composed of 

 very elongated slender crystals, as in 

 fibrous gypsum; and, 9, radiated, when 

 the fibres present a radiated or divergent 

 arrangement, as in actinolite slate. 



2. The texture of aggregated compound 

 rocks is said to be, 1, compact, when the 

 particles are so minute, as to give the 

 rock a dense, homogeneous appearance, 

 as in some kinds of granite and green- 

 stone ; 2, earthy, as in lava ; 3, granular, 

 as in clay and mari ; 4, crystalline, also 

 called granular or granitic by geologists, 

 as in granite and hornblende rock; 



5, sloty, as in gneiss, mica-slate, and 

 chlorite-slate ; this texture being crystal- 

 line in the compound rocks, but with the 

 component minerals more extended in 

 one direction than in another, and thus 

 arranged so as to form distinct laminae ; 



6, porphyritic, when in a basis, either 

 crystalline or compact, distinct crystals 

 are interspersed, as in various kinds of 

 porphyry, porphyritic granite, syenite, and 



