MINERALOGY. 



417 



Mict-iiiie. 



ides the beds above described, gneiss contain* 

 . i -.uiite, mica-aisle, and clay-slate. 



Glance L'val. The slaty kind sometimes occurs in 



,n gneiss. 



8. AlclaliiferrMS Mineral*. Gneiss is one of the 

 most metalliferous of the primitive rocks. The me- 

 tals occur in veins, beds, and imbedded masses, but 

 in greatest variety in vein?. 1 here are few metals 

 that do not occur in it. Most of the Saxon, Bohe- 

 mian, and Saltzburgian mines, are situated in this rock. 

 The oltleit gnei-s in the Saxon Erzgebirge, that with 

 reddish-coloured felspar, is the least productive in 

 ore-t; but the newer, with white-coloured felspar, is 

 the most productive; and the veins, though small, 

 are numerous. The oldest venigenous formation ap- 

 pears to be that which contains tinstone. The tin-ore 

 is accompanied with wolfram, molybdena, arsenic-py- 

 rites, fluor-spar, chlorite, topaz, and opal. The se- 

 cond venigenous formation appears to be lead-glance. 

 The third formation consists principally of copper, 

 and the ores arc gi*y copper-ore, copper-glance, 

 copper- p\ rites, and variegated copper-ore. The 

 fourth formation, which is very extensive, contains 

 <>f cobalt. The newest formation is that which 

 contains ores of silver. Veins, containing antimo- 

 ny and red ironstone, occur in gneiss, and these are 

 supposed to be newer than any of the preceding. 



of qmrtx with gold also occur in gneiss. 

 The metalliferous beds that occur in this rock con- 

 tain magnetic iron-ore, argentiferous lead-glance, 

 blende, copper an i ! to. 



Toe lead-mines of Mronuan in Argyllshire are situ- 

 ated in gneiss. 



_/,;; /i i al diilriliiitio*. It is a very widely dis- 



tributed rock. It is found in almost every country 



where granite occurs ; and is often interposed between 



granite and mica slate, or i* contained in mica-slate, 



or even in clay-slate. It is an abundant rock in Scot- 



land, funning extensive tracks in the middle and 



northern division*, and also in the island*. It is 



the principal rock in Sweden and Norway. It oc- 



cupies almost the whole of the Saxon metalliferous 



mountains: it abounds in Itohemia and Silesia ; it it 



not uncommon in t!ie Black Forest, the Upper Palati- 



nate. ...i. in the Southern Alps, the Pyrenee*, 



and the Voage*. It occur* also in Greece ; ami. in the 



>ens, the old mine- works of the ancient*) 



:i it. It is an abundant rock in the 



-t*te* of America, and in South America: 



with it in the i^li chain of the Andes 



of Quito, in the mountains of Parinu, and Venezuela, 



III. Mica- Stale. 



Gin- ter -",,. 



Micaceous Shistus. 



(** 



llMBt 



ste micace. Broikanl. 

 Rocke Feu;,, i tic, it quartz, ou Schist* micace. 



Daul/nuion. Sausiure. 



1 i mtilucnt Pnrtt This rock is composed of 



vjuartz, and, like gneis*, has a slaty struc- 



,ica it generally the predominating in- 



u'rey, sometimes inclining to 



(wen, *on ..w, aril more rarely to brow n. 



plates, not in distinct 



qusrtz is grey, with its n-ual 



<>u* lustre, aii<: t -,l ,,, "thin lenticular 



ma**es, inicrpoMd betweea the plates of mica. Some, 



VOL. XIV. r.KT II. 



times these masses increase in magnitude, and become Geognoijr. 

 globular, anil then the rock acquires a conglomerated ~~~{~~* 

 structure. Although the mica forms the princip.il and 

 predominating ingredient in mica slate, yet it some- 

 times happens that the quartz is the nio-t a'.nindant, 

 and thus a transition is formed into quartz rock. 



2. I'nrieties. We can distinguish different kind.s of Varieties. 

 mica-slate. These are Common, Undtila ed, Talrki), 

 and Fine Slaty. The comm-m is straight, and rutlu-r 

 thick slaty, and contains garnets, and sometimes fel- 

 spar. The undulated lias a waved structure, and con, 

 tains neither garnets nor feUpar. The talcky it 

 straight slaty; contains thick layers of quartz, and 

 the mica has a green colour, and inclines to talc. 1'he 

 fine ilafi/ borders on clay-slate, (the next rock in the 

 order of succession,) has a light yellowish grey co- 

 lour, and contains extremely little quartz ; it pa**e* 

 imperceptibly into clay-slate. Of these, the oldest is 

 the Common, and the newest the Fine-slaty. 



S. Imbedded Minerals. It frequently contains im- imbedded 

 bedded minerals of different kinds. The principal of mineral*. 

 these are the foUowing: 



(1.) Garnet, either in grains or in crystals, and is so Garnet. 

 frequent and abundant, that it may almost be con- 

 sidered as a characteristic and principal ingredient of 

 the rock. It abounds in mica-slate districts in Scot- 

 land, and on the continent of Europe. 



(t.) TumimtHmt and Schorl. These are met with in Tourmt. 

 the mica-slate of Scotland, and in other countries. im and 

 (3.) Gremalite. This mineral occurs in the mica- Schorl. 

 slate of the county of Wicklow in Ireland, and in Gf'"* 1 '**- 

 (li-trii-ts of the same description on the continent of 

 Europe. 



(4.) Chiattolilr. This curious mineral is found in Chias- 

 mica-tlate in the Pyrenees. tolitt. 



(5.) Kyanite. Is found in the mica-slate of the j^ Jut - lttt 

 Shetland islands, and also in a similar rock in Banff- 

 shirr. 



(6.) EmrralJ.The beautiful emerald, found in E- Emeral.U 

 gypt, occurs in mica-slate. 



Betides the minerals already enumerated, many 

 others, as vesuvian. rutile, graphite, &c. occur in 

 mica- slate. 



4. Stratification and Position. \l is very distinctly Stratitct- 

 stratified. The strata are sometimes variously convolut- tion md 

 ed, and the same character occur* in the substance of petition. 

 the strata. It often rest* on gneiss, and is covered by 

 clay-late. It passe*, on the one hand, into gneiss, 

 and the transition is made by the common kind ; and 

 on the other into day-slate, and the transition >- made 

 by the fine slatv kind. The out-goings of the strata 

 are frequently lower than those of the gneiss, on which 

 they rest, and higher than those of the clay- slate that 

 cover them. It sometimes also occurs in beds in 

 gneiss, and clay-slate, and even in grai 



5. Foreign Beds. It contain* more !' t i_rn bed* Foreign 

 than gneiss. The following have been observed : bej< - 

 Granular limestone, dolomite, hornblende-slate, and 

 hornblende-rock, actynolite, garnet, talc, serpentine, 

 chlorite, quartz-rock, magnetic iron-stone, magnetic 

 py rites, copper-pyrites, iron- pyrites, arsenic-pyrites, 

 blende. lead-glance, and red ironstone. 



(>. form of M The acclivities of the moun- Form of 



tains are gentle, but the cliffs it forms are not sorouuotaini. 

 considerable as those in gneiss mountains. U lirn mu- 

 ral precipices oci-ur, tli- y are seldom of great height. 

 The Mimmit* of the hills are round-bai ' 



7. A/etaflj/erosj* Mineral*. It is one of the most Metalliltr. 

 metalliferous of the mountain-rocks. The ores it con- ou * mintr - 

 3o " 



