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sidered as having always been the 

 bed of the ocean ; on the contrary, 

 what are now the most elevated 

 portions of the earth's crust were 

 once submerged, and over them the 

 ocean for ages rolled its majestic 

 waves. This is not an invention 

 of modern geologists, Ovid declares 

 the same : 



Vidi factas ex sequore terras ; 

 Et procul a pelago concha) jacuere marines ; 

 Et vetus inventa est in montibus anchora summis ; 

 Quodque fuit campus, vallem decursus aquarum 

 Fecit; et eluvie mons est deductus in a>quor : 

 Eque paludosa siccis humus aret arenis ; 

 Qusequesitimtulerarit.stagnatapaludibushument. 

 Metamorph. lib. xv. 



OCEA'NIC DE'LTA. A delta formed at 

 the mouth of rivers where they 

 enter the ocean, as distinguished 

 from either lacustrine or mediter- 

 ranean deltas. 



OCELLA'RIA. A genus of fossils, thus 

 described by Mr. Parkinson : " a 

 lapideous polypifer, expanded in a 

 membranous form ; variously con- 

 voluted and rather infundibuliform, 

 with an arenaceous surface, porous 

 on both sides; pores cylindrical, 

 in quincunx order, with a solid 

 axis in a raised centre." 



O'CELLATED. (pcellatus, Lat.) In con- 

 chology, applied to shells, when 

 marked with little eye-like spots. 



OCHRA'CEOUS. Of a brown yellow 

 colour, resembling ochre. Alter- 

 nating with an orchraceous iron- 

 stone. 



O'CHRE. (w'x i pa ) Gr. ocJira, Lat. ocre, 

 Fr.) Bed iron ore ; it yields good 

 malleable iron. Colours red, yel- 

 low, and brown. It occurs in dull 

 earthy masses, nearly or quite 

 friable, which soil the fingers. Its 

 constituents are oxide of iron 83, 

 silex 4, water 12. 



OCRY'NIAN. The Ocrynian formation 

 is not only distinguished by con- 

 taining shorl, but also by a great 

 excess of felspar, which forms the 

 principal constituent in nearly all 

 its rocks. 



OCTAC'DEAL. } Having eight sides 



OCTJLHE'DRAL. j all equal. 



OCTACDRITE. | Octaedral oxide of ti- 

 OCTOCDRITE. j tanium ; the Titane 

 anatase of Brongniart ; Octaedrit 

 of Werner ; Octaedrite of Jameson ; 

 the Oisanite of Lameth. A pure 

 oxide of titanium, crystallized in 

 acute, elongated octaedrons, con- 

 sisting of two pyramids, whose 

 faces are isosceles triangles, and 

 whose bases are squares. Colours 

 blue, blackish-blue and brown. 

 Lustre splendent and adamantine 

 Fracture foliated ; easily broken. 

 It scratches glass. Specific gravity 

 3 -8. Before the blow-pipe it is 

 infusible by itself, but with borax 

 it fuses into a glass. It occurs in 

 veins in Dauphiny, Norway, Spain, 

 and Brazil. 



OcTAe'DRON. } (o/cTaefy>os, from o/rra>, 



OCTAHEDRON, j eight, and edpa, a 

 side, Gr. octa&dre, Fr.) The solid 

 angles of an octaedron are formed 

 by four equal and equilateral plane 

 triangles ; consequently it is formed 

 by two equal spare pyramids joined 

 together at their bases, the sides 

 whereof are equilateral triangles. 

 The octahedron (unlike some forms 

 which are not susceptible of varia- 

 tion, as the die or cube, a solid 

 invariably bounded by six square 

 surfaces or planes) is susceptible of 

 variation ; it is sometimes flat and 

 low, and, at others, acute and high. 



O'CTOPUS. (from OKTW, eight, and 

 TTOV^, a foot, Gr.) A genus of 

 sepiae. The octopus was the animal 

 denominated polypus by Aristotle. 

 It has eight arms, all of equal 

 length, and contains in its interior 

 two very small rudimental shells, 

 formed by the inner surface of the 

 mantle. 



O'CTODENTATE. (from octo, eight, and 

 dentatus, toothed, Lat.) Having 

 eight teeth, and no more. 



O'CTOFID. (from octo, eight, andjindo, 

 to cleave, Lat.) Eight-cleft. In 

 botany, an epithet for a calyx di- 

 vided into eight segments. 



OCTOLO'CULAE. (from octo, eight, and 



