GRANITE. 



v.-hole group of mountains to wliich it belongs ; for though 

 lie faw large tabular mafl'es, fometimes nearly vertical, fcpa- 

 rated by filTures, they appeared to him to be much too irre- 

 <Tular, too little extended in length and height, and vaftly 

 too much in thicknefs, to be reckoned the elFefts of flrati- 

 lication. As in the third volume of Jamefon's " Syftem of 

 Mineralogy," Arran is not mentioned among the localities 

 where ftratified granite occurs, it would appear as if that 

 "■jognofiau does not lay any ftrefs upon his lirlt remark on 

 the natui-e of the above-mentioned mountain. 



The relative a«e of the different varieties of granite has 

 engaged the attention of feveral writers on geology ; but 

 it mull be faid, that mod; of the opinions that have been 

 broached on this fubjeft, and the various ideas entertained 

 by theorills refpedting .what they call regeneration of gra- 

 nite, are too vague, or at lead too little founded on adlual 

 obfervation, to be entitled to particular notice. Some geo- 

 loo-ifts on the other hand have abfolutely denied the exift- 

 ence of a fecond and third granite-formation. The Wer- 

 nerian fchool admits three diftiniJt formations of granite. 

 T\iefiijl or cUeJl is that which, of all rocks we are acquaint- 

 ed with, is funk the deeped into the interisr ot the earth, 

 and which therefore may with propriety be conlidered as 

 ibe fundamental rock. This oldeil granite alfo conditutes 

 thehighed parts of the furface of the earth, and, thus eleva- 

 ted, is generally furrounded, and, as it were, e^lvelopcd by 

 other primitive rocks. It is frequently coarfe -grained and 

 porphyritic. It occurs both dratified andimdratificd; and it is 

 the latterwhich is often feen in largcglobular didincl concre- 

 tions cf confiderable dimenlions, fuch as in feveral parts of 

 Bohemia, in the Fichtelgebirge, in the ifland of Arran, &c. 

 This formation is, of coarfe, far more widely extended 

 than thofe of amore recent origin, "^rhe fecond granite formalion 

 is conlidered as occurring only in veins wliich never reach 

 any of the newer rocks, but are confined to the olded for- 

 mation. Such granite is marked v\ith lefs regularity of 

 ftrufture, than what is obferved in the older formation ; at 

 the fame time that it furpafi'es the newed granite, both with 

 regard to the regularity of arrangement, and fuperior firm- 

 nefs of the condiment parts. The third, or r.e-wefi granite- 

 formation, is always found fuper-incumbcnt on older primi- 

 tive rocks, often in an unconformable and over-lying pofi. 

 tion : it alfo occurs in veins, which have been feen to inter- 

 fe£t or traverfe veins of the fecond granite formation ; as a 

 certain criterion of the greater relative age of the latter. Its 

 ftrufture, according to the charafterillic given of it by 

 profefibr Jamefon, is very irregular ; it has a deep red co- 

 lour, and contains fometimes grains of garnet, and often 

 fragments of various primitive rocks of various magnitude. 

 When it occurs in veins, thefe are, according to the fame 

 author, not conneCled with any rock beyond the drata which 

 they traverfe. Examples of this newed formation arc, that 

 at Greifendein, a large group of deep rocks between Elircn- 

 friederfdorf and Geier in the Saxon metalliferous mountains, 

 where the coarfe granular and irregularly aggregated granite, 

 compofed principally of feldfpar and quartz, with but a 

 fmall portion of mica, occurs reding on mica (late, in an un- 

 conformable and over-lying pofition : it contains neds of 

 <juartz and feldfpar, as alio fragnients of gneifs and mica 

 flate, from the fize of a cubic each, to that of loo cubic 

 feet and upwards Another indance of this formation we 

 Iiave in the tin dockwork at Geyer, where it is contained iu 

 a hollow of gneifs, and agrees in its charafters with that of 

 Greifendein. Ano'her portion of the fame formation, is 

 that at Johanngeorgendadt, Auerdjerg, and Eibcndock, 

 where, however, it occurs only in veins, which are from a foot 

 to feveral fathoms wide, and are ufually traverfed by metalli- 

 8 



ferous and other veins. Mr. Mohs has given a very good 

 charafteridic of this newer granite. Veins of the fame kind 

 occur alfo in Bohemia, Upper Lufatia, at Minella in the 

 Alps, in the Shetland iflands, in Glen Morifon, and in the 

 Highlands. 



The nature of the jud mentioned granitic veins iS- con- 

 fidered in a difierent light by Dr. Hutton, according to 

 whom all veins, whether they are obviouHy conneftcd, or 

 whether they have no appai'cnt connexion, with any large 

 mafs of granite, are coeval with, and conditute a part of the 

 main body of what is called the oldclt granite by the follow- 

 ers of the Neptunian fydem. Mr. Playfair has given leve- 

 ral e.'vamples of veins invilibly cc:me6ied with larger mafies ; 

 in thofe at the ille of Coll, in the Hebrides, at Portfuy, in 

 Cornu-all, in Glen Tilt ; and of fuch as are vifibly conncfled 

 with the m.ain granitic body, in thofe occurring iu the illand 

 of Arran, in Gallov/ay, in Invernefs-diire, St. Michael's 

 Mount, Cornwalh Mr. Jamefon, however, fays that he 

 has convinced himfelf, after a very careful examination of 

 the rocks of the illand of Arran and of Galloway, that 

 they do not afford a fuigle indance of granite veins, 

 Ihooting from the olded granite into the adjacent rocks, 

 nor of veins ti'averfmg newer primitive rocks, as it 

 has been infinuatcd to be the cafe with the granite veiris 

 in Glen Tilt. The fame author obferves oi this occafion, 

 that veins of feldfpar have been frequently confounded 

 with granite veins, and he fubjoins fome obfervatious on 

 this fubjeil communicated by the late Dr. Mitchell, accord- 

 ing to which there is a mod palpable difference between fup- 

 pofed and genuine granite veins ; the former being frequent- 

 ly narrower than one inch, and commonly much ramified, and 

 fometimes tortuous ; but they condantly adhere mod firmly 

 to the adjacent done, and when they contain apparent frag- 

 ments, the flaty drudlure of thefe is ever conformable to that 

 of the contiguous rock ; while genuine granite veins never 

 fill (hort of tome inches, are always pretty ftraight, feldom 

 giving off branches : they have a dillindt feparalion, and 

 contain fragments of the adjacent rock, which lie prcmifcu- 

 ouHy ; the granite is conllantly uniform, containing the 

 three ingredients equally mixed ; and Dr. Mitchell has 

 always found it fmall-grained. The fuppofed granite, ac- 

 cording to him, coufids of feldfpar, of a very unequal grain, 

 inclofino; fometimes fpotsof mica, and rarely fpecks of quartz. 

 From all which this mineralogid concludes, that the lad men- 

 tioned veins are nearly of contemporaneous origin v\ ith the 

 I'ocks in which they are contained, and ought, therefore, to be 

 confidared as, and called, feldfpar veins. 



Although granite is the harded, and one of the mod du- 

 rable rocks we are acquainted with, it is, neverthelefs, fub- 

 jcCt to di/iiitegri'lion, which manifeds itlelf not only in the 

 crumbling of the furface of the expofed parts of granitic 

 beds, but likewife in the feparatian of vail maffes, which, 

 being di united by the enlargement of the rents and fiifures 

 that genei'ally traverfe the granitic mountains, or crofs the 

 drata in a nearly vertical direction, ai-e partly precipitated 

 from their high iltuation, partly difplaced in various manners, 

 fo as to produce the appearance of huge artificial ilrutUires, 

 and of other objefts to which the fancy of the beholder may 

 compare them. 



M. De Luc has feen on the Riefenbirge, in Silefia, a mmi- 

 ber of pillars produced by fuch difintegration, both.folitary 

 and grouped together, in a draight hne, and, at a diilance, 

 prefenting the appearance of many higli piles of gourds. 



The Adon-iliolo mountains in Dauria, which coniiil of 

 granite, are, according to Pallas, in many parts broken into 

 all manner of (hapes, rcprefenting vad ruins, grottos, and 

 jmmenfe flat maflcs piled on one another in all dire6tit>ns. 



Several 



