GEOLOGY. 



cwnfidcrcd \'.ith regard to thtir dejlroying, and, in confequence 

 '>f tin's dellruclioii, with regard to their forming effects. 

 The waters of the ocean potfefs the former of thefc powers 

 in a fuperior degree ; wliole maritime dillricls are known to 

 h;iv.- bpi-n overwhehned by their irregular action upon the 

 Ufid ; but alfo the regular motion of the fea, ebb and flood 

 tide, currents, &c. confiderably contribute to gradu- 

 lUv changing the face of tlie bottom of the fea, and of 

 the ihores on which they adl. The dellroying eftecls 

 of the atmoipheric waters are both mechanical and che- 

 mical ; the former are produced by long continued rain, 

 watcr-fpouts, ice, fnow, thaws, and confequent floods, 

 by which confiderable psrtions of rocks are detached and 

 carried, together with other loofe materials they meet, 

 t» more or lefs dillant places, according as the bulk of 

 thefe materials or tlie nature of the country, either 

 favours or impedes their progrefs. The chemically deftroying 

 effects of water are lefs rapid, and depend on the folubihty 

 of the different rocks over which they flow. T!ie forming 

 effefts of v.-ater, both mechanical and chemical, are the 

 nitural confequence of its delb-uCtive cfFecls ; examples of 

 tlv; former are fandbanks, changes of coafts, &c. Of the 

 latter, beds of fait, calcareous, and other depoiltions, &c. 

 See Waters, AtmofpL'ru; and OrEAx. 



The effects of volcanic tire are deflroving by means of the 

 confumption of the inflammable materials, by deficcation 

 and fufion ; and forming by fublimation, and by the pro- 

 duftion of lavas and other volcanic ejections, by fublima- 

 tion, &c. See VoLCAMO. 



From the defcription of the inequalities of the furface of 

 th? earth, and of the means employed in forming them, the 

 V/erncrian fcliool proceeds to tl.econfideration of the internal 

 ilruCture of the earth, the knowledge of which we derive 

 from a careful examination of the order which nature has 

 ftfUowe'l in the dcpofition of the mountain malfes, and which 

 is principally laid open to view in the chalms and fections 

 produced by floods, &c. in natural caverns and in the interior 

 of mines. By ihele nie.jis we may become acquainted with 

 four different llruc"lures, ber.des that of the iimple foffil, 

 which is the objeCl of Orydlognofy ; i. The flrutlure of 

 rocks or mounia'iii rods ; thefe are either fimple (fuch as lime- 

 lione, clay-flate, ferpentine), or aggregated, in which cafe 

 the principal kinds of texture of tlie component parts are 

 granular, fiaty, porphyritic, and amygdaloidal. (See RorKS. ) 

 2. A more general llruclure is that of mountain mojfcs ; thefe 

 have either a Umply flra'ifisd llrufture, -jiz. when a moun- 

 tam, or movmtain mafles are compofcd of one fpeeies of 

 rock divided into parallel tabular maffes or flrata ; or they 

 confiil of alternating itrata of different rocks, v%-hich in this 

 cafe are called btds. Mount'.in maffes alfo difphy what is 

 termed yJ^.-'.-c-i/flrufture, in which diffinft concretions on a 

 .age fcale are obfervablc, fuch as the columnar, the large 

 .^lobular, and the club-fhapcd ftructure, feveral modifications 

 of which are obferved in bafalt. Another variety of this 

 lirufture is called tabular feameJ ftrufture, which is not 

 unlike flr.-.tificatioa. (See ^Icu^■T.'VI^^ Masses, and Stra- 

 ta. ) A iliil '.T.ore general flructnre is ^. The Jiruliure of 

 / rmjtions, wh'.ch term AVerner applies to a determinate 

 .i;i'cniblage of feveral fimilar and diJumilar rock maffes which 

 conflitute an independent whole. If the mafs -is uniform 

 tl roughout ; if, for inftance, it confil's entirely of fand- 

 li.>ne, granite, &c. it is ti rmed JimpU, whereas it is a com- 

 ponnd form.ation, if it exhibits diflimilar maffes, fuch as black 

 coal with fletz-trap, &c. Some formations ccnllitute the 

 principal mafs of a mountain in which they occur, (gnelfs, 

 clay-dale, porphyry, f<c.) while others occur only imbedded 

 (j.crphyry, lime-ftone, &t.) ; ar.d thefe b«is, if they occur 



in different principal formations, and always under the fame 

 circumflances, notwithllanding the difference of the rocks in 

 which they are found, and if, moreover, they form members 

 of a lenes of formations, are confidered as, and deno- 

 minated /Wf^i'«(i'«/ybnna/;!;n/. If the reverfe of all this IB 

 obferved in fingle beds, they are called fulorj'inah- to the 

 formation in which they are imbedded, as is the cafe with 

 the beds of roe-Rone, in the fecond fand-flone, &c. For 

 fome further diftinctions, fee RF.HOsnOKn;.s, mUicial. The 

 mofl general of the flructurcs we know is, 4. That of tke 

 crujl of the earth, conipofed of rock formations, which cover 

 each other in certain directions, and in a regular manner. As 

 to the original extent of forroatii-ns in general, Werner terms 

 uni'verfal tormations thofe which, without great interruption, 

 furroand the whole globe, and thus conltitute the greater 

 part of its cruil ; to it belong almoft the whole of the pri- 

 mitive, tranfition, and ffet/.-formation. Pailial formations, 

 on the other hand, are thofe that appear only in detached 

 fpots, and exhibit cliarafters dilHnct from thofe of the 

 univerial formation : thus the depofition at Wehrau in Lu- 

 fatia (which Werner fufpecls to be the refuk of a fniall and 

 partial flood) is compofed of fand-ltone, lime-ftone, bitu- 

 minous fliale and iron-clay, which all re!l on loofe fand. The 

 prefent extent and continuity of farmations are fo far different. 

 from the original, that thofe called vmverfal often appear 

 broken into fmall detached portions, frequently refembling 

 partial formations, and they receive different names according 

 to their different fhapes, and the fituations in which they are 

 found. Other conliderations relative to the ftruclure of 

 the crufl of the globe are derived from the pofition and di- 

 racllon of the flrata in regard to the fundamental or fub- 

 jacent rock, from the diredtion of the flrata without reference 

 to the fundamental rock, and from the relation of the out- 

 goings (/'. e. the up])er extremiiics of the diflTcrent flrata as 

 they appear at the furface of the earth), to the exterior of 

 the mountain ; for vehlcli fee Stkata. 



A comparifon of the different clalfes of rocks, and thcfr 

 fucceffion and Uratification, poijits out the following dif- 

 tinctions. The clafa of rocks on which all others reil, and 

 which, on that account, is confidered as the oldeft, is tlie 

 clafs of the primitive reds, whofe texture is often more 

 or lefs cryllalline, a quahty denoting preuous che- 

 mical foiuticn. They comprehend granite, gneifs, mica- 

 flate, talc-flate, hornblende flatc, fyenite, porphyry, ferpen- 

 tine, and lime-llone. Thefe rocks are moftly difpofcd in 

 conformable and unbroken ilratiiication, each newer flratum 

 with lov/er level, as is the cafe with gn.ifs, mica-flale, and 

 clay-flate, while the granite beneath will fometiaics appear 

 to rife up through thtm, cnconipafTed, in various manners, 

 by the other rocks. (See Rocks, Primitive.) Tlie rocks 

 next in fucceffion are fuch as are likewife principally ccin- 

 pofed of chemical prodadlions, but in which mechanical 

 depofition is obferved more abundantly the nearer tliey ap- 

 proach tht following clafs ; the rocks conftituting this in- 

 termediate clafs are called tranfition-rocks. I_ime-flone 

 occurs more frequently in this than in the preceding clafs ; 

 the other rocks it contains are principally grey-wacke, 

 grey-wacke flate, and clay-flale. (See TRANSlTiOX-iJc.'//). 

 To this fucceeds, as of ilill later origin, the clafs of fletz- 

 rocks, in which the mechanical depofits occur in greater 

 abundance, at the fame time that the chemical precipitation 

 difappears. (See YLHiz-Rods.) The next clafs which 

 bears the charaiSer of (lill more recent formation, is en- 

 tirely compofed of mechanical depofits, fuch as fand, clay, 

 &c. See Rocks, y^//h7'i<i/.) But, befides thefe formations, 

 the outgoings of which fhow gradually diminiihing levels 

 from the older to the newer, there are two others, the llrata 

 i of 



