UNI 



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U P P 



epidermis, bivalves ; they are com- 

 monly called freshwater muscles. 



UNIVALVE, (from unus, one, and 

 vaka, a shell, Lat.) A shell which 

 is complete in one piece. The Lin- 

 nasan arrangement of shells consists 

 of three orders, namely, multi valves, 

 bivalves, and univalves. Univalves 

 are far more numerous than either 

 multivalves or bivalves, both in 

 genera and species. 



UNMA'LLEABLE. That cannot be ex- 

 tended by hammering; that cannot 

 be hammered out into plates or 

 laminae. 



UNORGANIZED. Having no parts in- 

 strumental to the motion or nour- 

 ishment of the rest. 



UNSTRA'TIFIED. A term applied to 

 rocks that are not stratified, or not 

 arranged in strata. "When no traces 

 of beds can be detected, and the 

 rock merely forms a great mass of 

 mineral matter, without other lines 

 than those of cleavage, it is said to 

 be unstratified. De la Beche ob- 

 serves, "the terms stratified and 

 unstratified have been commonly 

 considered as respectively synony- 

 mous with aqueous and igneous. 

 Practically, this division is highly 

 valuable; but theoretically, it is 

 not so satisfactory, at least, if we 

 are to infer that all rocks divided 

 into tabular masses, one resting on 

 another, must have been deposited, 

 either chemically or mechanically, 

 from water. We should be careful 

 not to couple too far stratification 

 with aqueous deposition, as sheets 

 of igneous rocks may cover pre- 

 existing sheets of similar rocks, 

 and the result be stratification." 



UPPER GREENSAND. (Glauconie Cray- 

 erne, Fr. (Moritische Kreide, Germ.) 

 A member of the cretaceous group. 

 An arenaceous rock, for the most 

 part very calcareous, containing 

 grains of silicate of. iron. The 

 upper greensand is a marine deposit, 

 consisting of marly stone and sand, 

 with numerous green particles, fre- 



quently including concretions of 

 chert, and, in some places, beds of 

 stone. From the application of 

 portions of this deposit in the con- 

 struction of ovens, furnaces, &c., 

 it has obtained the name of Fire- 

 stone. The situation of the upper 

 greensand is between the chalk 

 without flints above, and the gault 

 below. Its thickness is about 100 

 feet. 



UPPER LUDLOW ROCK. A sub- division 

 of theLudlow formation, thus named 

 by Sir R. Murchison. This great 

 explorer of the silurian rocks says, 

 "this sub-division of the Ludlow 

 formation consists essentially of 

 thin bedded, lightly coloured, and 

 very slightly micaceous sandstones, 

 in some parts highly argillaceous, 

 and in others so calcareous as to 

 assume the character of impure 

 limestones. When deeply cut into, 

 these beds are of greenish-grey or 

 bluish-grey tints, but they rapidly 

 weather to an ashen or, more rarely, 

 to a rusty-brown colour." 



UPPER SILURIAN ROCKS. Sir E. Mur- 

 chison divides the Silurian rocks 

 into upper Silurian and lower Silu- 

 rian. The upper Silurian comprise 

 the Ludlow formation, sub-divided 

 into the upper Ludlow, the Aymes- 

 try limestone, the lower Ludlow, 

 the Wenlock limestone, and the 

 "Wenlock shale : the lower Silurian 

 rocks comprise the Caradoc sand- 

 stones and the Llandeilo flags. 

 " The two formations," he says, "of 

 Ludlow and "Wenlock, possess so 

 much of a common lithological 

 aspect, and offer such intimate 

 passages from one to the other in 

 the distribution of the organic 

 remains, that they form a very 

 distinct natural sub-group, which 

 I have termed upper Silurian." 



U'PPER TE'RTIARY STRA'TA. These 

 strata are considered to be of more 

 recent origin than those usually 

 denominated tertiary, and, by some 

 geologists, have been termed qua- 



