GEO 



of which, inftcad of having pnrallchfm with, are fuiierincum- 

 hcnt on, the outgoings of the other flrata : they are called 

 the iwx'ejl ficl':^-irap, and the r.eivtr porphyry fornirj'ion, and 

 are feen to reft both on flctz-llrata of very recent formation, 

 and on elevated primitive mountains. The former of thefe 

 formations is particularly interefting, as including rocks,^ 

 ^vhofe origin has been, and continues to be, a fubjed oi 

 controverfy between the Neptunifts and Volcanifts, I'uch as 

 bafalt, wacke, &;c. all of which, according to Werner, are 

 the refults of a deluge, or fudden rife of the water at a 

 more recent period than that in which the iletz-mountains 

 were formed. (See VLZTZ-Roch and TuAP-Formnlioii.) 

 The fecond of thefe great formations, occurring in the 

 lame unconformable Itratilication, confifts of porphyry, 

 fyenite, and pitch-ftone, and is fuppofed of much older 

 origin than the ncweil fletz-trap-formation, with which, 

 however, it agrees in many refpe-Ss. See Pokphvrv. 



No geologill before Werner has pointed out the fuccef- 

 fion in which the different fuites of formations have been 

 depofited from the water at different periods ; a fucccfiion 

 which (hows the aherations that fluid has undergone with 

 regard to the fubftances it held, at different tmies, citlier 

 chemically diffolved, or mechanically floating. Thus the 

 oldeft of the primitive rocks contain metals almoft peculiar 

 to them, and which, therefore, were not again depofited m 

 fucceeding periods, fuch as tin, molybdena, and tunglleen ; 

 and in feveral cafes, one and the fame fubiiance, (luch as 

 lime-done,) though it be repeated at confiderable intervals, 

 ilill adopts in each of them a peculiar characler. Thele 

 fuites are, I. That of the liimjione formation, beginning 

 with tlie primitive crylfalline granular hme-llone,_ and 

 pafling, by infenfible gradations, through the tranlition, 

 and fletz-lime ftones, into the lowermoll links of the ferics, 

 i,iz. chalk and calcareous tuf. 2. That of the Jlate form- 

 ation : its central point is clay-flate (from whicii this 



GEO 



members, the lird or older occurring with primitive rock';, 

 efpccially pi-imitivc lime-Hone, in conformable ttratification ; 

 and the fecond or newer, found in an unconformable 

 and overlying pofition on the older rocks. See Seiipek- 



TIME. 



For further particulars relating to the Wernerian fyftcm 

 of geognofy, we refer to the articles Strata, Vein, and 

 WiVTERS, Diminution of. 



GEOMANCY, Geo.maxtia, a kind of divination, per- 

 formed by means of a number of little points, or dots, made 

 on paper at random : and confidcring the various lines and 

 figures which thofe points prefent : and thence forming a 

 pretended judgment of futurity, and deciding any c^ueftioa 

 propoied. 



The word is formed of the Greek yr,, terra, earth ; and 

 jxry.-.-^iij., divination ; it being the ancient cullom to call 

 little pebbles on the ground, and thence to form their 

 conjedlures ; inftead of the points afterwards made ule 

 of. 



Polydore Virgil defines geomancy a kind of divination 

 performed by means of clefts, or chinks made in the ground ; 

 and takes the Perfian Mairi to have been the inventors 

 thereof. 



GEOMETRICAL, fometliing that has a relation t>. 

 geometry. 



Thus we fay, a geometrical method, a geom.etrical genius, 

 geometrical ftritlnefs, geometrical conitrucxion, geometrical 

 demonllration. 



Geometry itfelf fcems to lead us into errors ; after once 

 reducing a thing to geometrical confideration, and finding 

 that it anfwers pretty exacftly, we purfue the view, are pleafed 

 with the certainty and agreeablenefs of the demonf^rationo, 

 and apply the geometry farther and farther, till we often out- 

 run nature. 



Hence it is, that all machines do not faccced : that all 



formation derives its name), paflmg, on one hand, through compofitions of mufic, wherein the concords are the mod ri 



rnica-flate into gneifs, when the ilaty ftrudure gradually 

 difappears, and a pafTage is formed into the olded member, 

 namely granite ; and, on the other hand, tlirough tranlition. 

 flate, grey-wacke llate, and grey-wacke, into the feri'es of 

 fletz fand-!ioncs, and from thence into the alluvial feries, 



gidly obferved, are not agreeable : that the mod exaft adro- 

 nomical computations do not alwjiys foretell the precife time 

 and quality of an eclipie, &c. 



The reafon is, that nature is not a mere abdraft ; mecha- 

 nical levers and wheels are not geometrical lines and circles ; 



confitting of (late clay, loam, fand, and gravel, 3 The trap- as they are often fuppofed to be : the talle for tunes is not 

 formation fuit.' pafTcs from the primitive horiiblende-ilate, the fame in all men ; nor at all times in the fame man: and 

 charatferized by its crvdHJlino nature, and from the pnmi- as to adronomy, as there is no perfcft regularity in the mo- 

 tive "■reen-done, and green-ilone flate, through the tranfition tions of the planets, tlicir orbits hardly feera reducible to 

 grcen-ftone, into the flctz-trap, formed ch'iefly of amygdaloid, any fixed, known figure. 



and from thence into the neweil fletz-trap formation, con- The errors, therefore, we fall into in adronomy, mufic, 

 fidin? principally of bafalt and wacke, unconformably fuper- mechanics, and the other fciences tq which geometry is ap- 

 inctvmbent on rocks of various antiquity. 4. The porphyry plied, do not properly arife from geometry, which is an in- 

 formation fultc is equally chara6teriinc in its different mem- fallible fcience, but from the falfe ufcj or th.e mifappKcation 

 bers, from old primitive porphyry down to that mentioned of it. 



" " " ■ ■ ■■' ■' "^ °^ '"'" ^ " Geometrical ConJlruHion of an equation, is the con- 



triving and drawing of lines and figures, whereby 

 to demondrate the equation, theorem, or canon, to be 

 geometrically true. See CoNiTllUCTiON of Equations. 



Geometrical Line or -Curve, called alfo algebraic line or 

 curve, is that wherein the relations of the abiciflas to the 

 femi-ordinates may be exprefhd by an algebraic equation. 

 See Curve. 



Geometrical lines are didinguidied into claffes, orders, or 

 genera, according to the number of the dimenfions of the 

 equation that cxprclTes the relation between the ordinatcs 

 and tlie abfciflas : or, which amounts to the fame, accord- 

 ing to the number of points in which they may be cut by a 

 right line. 



^_^^^_,^^ ,._ ^_ , , Thus aline of the fird order v.'ill be only a right line: 



feriKH'-n formation fuite licom^ok^j^i: far as we know, of two thofc vf tlie fecond, or c^uadratic order, will 'be tne circle. 



jftSove, as of fimilar origin vv^ith the newed fletz-trap form- 

 ation : the nature of the different members of this formation 

 fland, however, in need of further examination. (See 

 PoRPHvaY.) 5. The gyps formation comprifes three prin- 

 cipal memberc!, the ohlelt of which, or the primitive gyp- 

 fum, occurs in mica-flate and clay-flate ; the fecond and 

 third are fletz-gypfum, the form.er of them accompanying the 

 following, or 6, Saltformation, which conditutcs twoj.eries, 

 one of which occurs only^ with fletz-gypfum, (fee Fletz- 

 Rochs), while the other is dill forming on the bottom of 

 lakes, &c, (See liacK-Salt) 7. Thti coa'.formatirjn fate, 

 comprifing, belides the independent -coal formation, various 

 varieties of coal belonging to the fletz-trap formation, and 

 to alluvial d^'pofitions; the members of this fuite require 

 farther inveftigation. (See Yl^t/.-RocIs, and Coal.) 8._The 



