peel technique . A method of preparing rock sections for study. A smooth surface is differentially etched with acid, and then covered with cellulose acetate or a similar liquid that will dry to a transparent film. When this film is peeled off, it brings with it a thin layer of rock substance, preserving this material in its original space relations. It may then be studied microscopically.
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vanalite (van'-al-ite). A bright yellow-orange monoclinic mineral: NaAl8V10O38•30H2O .
anthrinoid (an'-thri-noid). Vitrinite that occurs in noncaking anthracites and that has a reflectance higher than 2.0% (ASTM, 1970, p.19). Cf: xylinoid; vitrinoid.
convection [meteorol] . (a) Transfer of heat by vertical movements within the Earth's atmosphere owing to density differences caused by heating from below. (b) The mixing and transport of properties other than heat. Cf: advection [meteorol].
monument [surv] . A natural or artificial physical structure that marks the location on the ground of a corner or other survey point; e.g. a pile of stones indicating the boundary of a mining claim, or a road or fence marking the boundary of real property. See also: boundary monument.
spilitization (spi''-lit-i-za'-tion). Albitization of a basalt to form a spilite.
Saurischia (Saur-is'-chi-a). One of the two orders of archosaurian reptiles commonly treated as dinosaurs, characterized by a triradiate pelvis. It includes bipedal predators (Carnosauria, Coelurosauria), quadrupedal long-necked herbivores (Sauropods), and presumptive ancestors of the latter (Prosauropoda). Range, Middle Triassic to Upper Cretaceous. Cf: Ornithischia.
principal point . (a) The foot of the perpendicular from the interior perspective center of a lens to the plane of the photograph; the geometric center of an aerial photograph, or the point where the optical axis of the lens meets the film plane in an aerial camera. Symbol: p. See also: fiducial mark; photograph center. Syn: center point. (b) Either of two points on the axis of a lens such that a ray from any point of the object directed toward one principal point will emerge from the lens in a parallel direction but directed through the other principal point. (c) The point at which a principal visual ray intersects a perspective plane.
bedding void . An open space between successive lava flows, formed where an overlying flow does not completely conform to the solidified crust of lava beneath it.
palimpsest [meta] . adj. Said of a structure or texture in a metamorphic rock in which remnants of some pre-existing structure or texture, perhaps even the original one, are preserved, and sometimes even megascopically visible. The term was first used by Sederholm (1891). Cf: relict [meta].