Page:The New International Encyclopædia 1st ed. v. 17.djvu/227

ROCK. 205 ROCKEFELLER. before consolidation ami was pounMl out cither as a broad layer (sliect) or as a stream, the rock jirodiiced is described as of extrusive, ell'usive, or volcanic origin. See lG.E0fs KocKS. The division of metamorphic rocks is com- posed of types developed from processes of alter- ation out of orisjinally igneous or sedimentary rocks, but it includes not only those rocks which may be traced to the one class or tlie other, but also those the origin of which is in doubt. To- gellier the several tj'pes of this division are de- scribed tinder the name crystalline schists, of which gneiss (q.v. ), schist (q.v.), and phyl- lite are the most abundant members. See ilETA- JIORIMIIC ROCK.S. Unaltered sedimentary rocks are further sub- divided into those of mechanical, chemical, and organic origin. Of the first mentioned class are the greater number — the true sediments and the a^olian deposits. Sand and gravel, greensand, loess (q.v.), clay, breccia (([.v.), conglomerate (q.v.), graywacke (q.v.), and shale (q.v.) have this derivation. Of chemical origin are the silice- ous sinters such as are to-day forming about the geysers in the Yellowstone National Park; the calcareous sinters of caverns in limestone, in- cluding stalactites, travertine (q.v.), veinstones, deposits of gypsum (q.v.), and limonite (q.v.), and the many rocks of concretionary structure known as oijlite (q.v.). Of organic origin are chalk (q.v.), flint (q.v.), shell limestone, and chert (q.v.). JIarl (q.v.), cement rock, litho- graphic stone (q.v.), and the several varieties of peat (q.v.) and coal (q.v.) have also an organic origin. The larger masses of compact limestone (q.v.) and magnesiau limestone or dolomite (q.v.) are known to have an organic and gen- erally also a marine origin, but the exact man- ner of their formation is a problem regarding which there are many opinions. The calcareous ooze which is now forming over the deep-sea bottoms is composed almost entirely of the tests of pelagic organisms, whereas such structures are found in the rocks only in chalk, a formation of comparatively rare occurrence. It has been sug- gested that the compact limestones which are so generally composed of crystals of calcite are produced from the resolution of the remains of these organisms now collecting npon the .sea bottom, perhaps even at the bottom of the ocean in the layers beneath the deposit of ooze. It is certain that a deposit of compact limestone is forming directly from Avater in the Everglades of Florida; and it is inferred that this process is a more or less widely distributed one. Lime- stones may, however, form from the evaporation of an inclosed sea. as has happened in past geo- logical ages within the area of the Western United States. IMechanical Sediments Classified on Basis OF Composition. The great class of mechanical sedimentary rocks are classified on the basis of their dominant constituent as arenaceous or siliceous rocks, argillaceous rocks, and calcareous rocks. The first mentioned rocks contain much quartz or silica ; those of the second class abound in clayey material, the base of which is a sili- cate of alumina and hvdrogen (kaolin or china clay) (q.v.), while the class of the calcareous rocks are essentially composed of carbonate of calcium, or of calcium and magnesium in the form of the minerals calcite, aragonite, or dolo- mite. Arkose, graywacke, sandstone, conglomer- ate, snnd, and gravel are the more abundant siliceous sedimentary rocks. Kepresentatives of tlie nrgillaccous rocks are arglUile or nuidstonc, shale, clay, mud, and silt. -Marl and calcareous shale are calcareous-argillaceous .sedinient.s and form a transitional member connecting the argil- laceous with the calcareous sedimentary rocks. Under the calcareous sediments are included limestone and dolomite, chert, etc. See Aiienace- ous Rocks; .:Vrgili.aceous Rocks; Calcareous Rocks. Bibliography. Diller, "The Educational Series of Rock Specimeas," liuUeliii Xo. I'tO, Uniltd l<latcs Geological .S'ldrr.i/ (Washington, 18!I8) ; Kemp, Hund-Book of liockx for Use M'ilhoiit the Microscope (New York, lS9(i) : Marker, I'clrol- oijy for •Stiidrtitf: (Cambridge, England, 181)5). ROCK BADGER, or Rock R,umiT. See IlyiiAX. ROCK BASS. A gamy and excellent bass {Amhlopliles rupestris) of the Northern States and Jtississippi Valley, called also 'redeye' and 'goggle-eye.' It is a foot long, olive green, with a brassy tinge and much dark mottling, and a black spot on each scale, forming interrupted stripes, the young irregularly barred and blotched. These bass are found in clear streams and lakes, where they keej) about rocks or sunken logs. See Plate of Bass. ROCK BUTTER. A name given to a variety of the mineral halotrichitc. It is a yellowish butter-like substance that is found as an elflo- rescence or exudation from some alum slates, notably those at Hurlet and Campsie, near Glas- gow, S'cotland, and at Rossville. Kielimond Coun- ty, N. Y. It is called also ntountain hutlcr. The name has likewise been applied to certain varie- ties of the mineral chrismatite. ROCK-COCK. A South American bird, more usually called cock-of-thc-rock (q.v.). It is a type of the genus Ruflcola, but was formerly in- cluded among the related pipras. ROCK-CRAB. An indefinite general name for a variety of crabs customarily living on rocky bottoms, as, along the New England coast, the Jonah crab. The name belongs rather to the family Cancridae, in which belong more common edible crabs than to any other group. ROCK CRYSTAL. A colorless, transparent varietv of crystallized quartz. The name is applied chiefiy to the massive varieties, such as Brazilian pebble, which is used for lenses ; but it also includes the small distinct crystals which are sold as imitations of the diamond and are called variously Bristol diamonds, Lake George diamonds, etc. The name is likew^isc sometimes extended to the violet variety of quartz or ame- thyst, to the red variety or Bohemian ruby or Siiesian ruby, to the yellow variety or citrine or false topaz, 'and to the brown variety or smoky quartz. Specimens are sometimes found con- taining inclusions of hair like or needle-like crvstals of other minerals such as actmolite, asbestos, epidole, gothite, hornblende, rutile. tour- maline, etc., which are called variously by the names of Cupid's arrous. Cupid's nets, Tlictis's hair-stotic, Venns's hairstoyic, etc. ROCK-DOVE. A wild dove of Western Eu- rope [Cohimhii liria). See PlOEON. ROCKEFELLER, John Davison (183ft—). An American capitalist, born in Richford, Tioga