7. Metalliferous illinerals.—Clay.slate is rich in me tals. It contains many of the venigenous formations that occur in the preceding primitive rocks, as tin, lead, cobalt, and silver. Very considerable metalliferous beds also frequently occur, and these contain copper pyrites, red copper-ore, copper-green, blue copper, malachite, iron-pyrites, magnetic pyrites, glance-cobalt, grey cobalt ore, arsenic-pyrites, blende and lead-glance. Gold also occurs in this formation, and it is said also cinnabar.
8. Geographical distribution.—It is a very widely ex tended rock. In this country, it skirts the Highlands from Lochlomond by Callender, Comrie, and Dunkeld ; in the whole of that extensive district, resting on and gradually passing into mica-slate ; the same appearances are to be observed in many other quarters in Scotland. On the continent of Europe, it has been traced through a great extent of country ; thus it occurs in Saxony, Bohemia, Silesia, Franconia, Bavaria ; the Alps of Swit zerland, Austria, Hungary, and many other parts in Europe. It occurs also in considerable quantity in North America, as Pennsylvania ; also in immense quan tity in South America ; thus it is said, that nearly the whole country betw:cri Potosi and Lima is compo,ed of it. In some of the districts above enumerated, tran sition clay-slate has been confounded with the primitive kind.
V. Primitive Limestone.
Ur. Kalkstein.—lf erner.
Primitive Limestonc.—Kirwan. Primitive Li m estone.—Jameson. Calcaire Primitif.—Brochant.
C'haracters.—This is a simple mountain rock. Its most common colours are snow, yellowish, greyish, greenish, and reddish white ; it is sometimes also grey, and the newer varieties incline to yellow. Its struc ture is always granular. Those varieties which arc associated with granite and gneiss are generally more crystalline than those contained in mica-slate and clay slate ; and, in general, primitive limestone is more crys talline than secondary. Werner remarks, that in the oldest members of the series, that is, in those contained in granite, the colour, of the limestone is pure white, translucent, and coarse granular ; in the newer members, the colour is less pure, the translucency less considera ble, and the granular distinct concretions smaller ; and in the newest, the concretions are so small as only to be discoverable by their glimmering lustre.
2. Imbedded Minerals.—It frequently contains acci dental ingredients, and these occur more frequently in the older than in the newer members of the series. We shall mention some of these : 1. Quartz. It occurs in massive pieces of greater or less magnitude, and some times also in crystals. 2. Mica. It sometimes occurs in such quantity as to give the stone a slaty fracture. These
two minerals, namely, quartz and mica, are the most common accidental minerals that occur in primitive limestone. Those of less frequent occurrence are the following: common hornblende, actynolite, asbest, ser pentine, augite, talc, steatite, felspar, epidote, tremolite, garnet, calc-spar, slate-spar, and pyrites.
3. Stratcation—It occurs more or less distinctly stratified, It was once the opinion, that granular aggre gated stones, as primitive limestone, granite, sienite, and greenstone, were never stratified. This, however, is a mistake. Primitive limestone also occurs in beds of greater or less magnitude ; sometimes these beds are short and thick, and are then said to form lying masses (liegende Stocke;) or the beds are so thick as to form whole mountains ; but this latter is a rare occurrence.
4. Formations.—There arc several formations of pri mitive limestone. Thus it forms one formation in gra nite, another in gneiss, a third in mica-slate, and a fourth in clay-slate. It is more abundant in mica-slate than in granite or gneiss, or even in clay-slate.
5. IlletallIferous Minerals.—It frequently contains ores of different kinds, and these occur often in beds, but seldomer in veins. The metalliferous beds contain ores of different kinds, as lead-glance, blende, magnetic iron stone, magnetic pyrites, auriferous arsenic pyrites, and native gold. The veins are very inconsiderable, and by some mineralogists are said to contain principally man ganesc.
6. Several beautiful varieties occur in this country. as in the islands Tirce, icolmkill, and Skye ; also in Pent shire, as in Glen Tiit, in Assynt, in the count! of S ,Lhcr land, and many other places. The promuntol!. lit A s, in the Archipelago, is said to he kollyustd of p,ii. IL VC limestone; also the Ishnci of Pi u!..„.nd pert o mt. A pc. nines, as about Carrara and Massa, many parts of tt I. .41:zme.—The name trap is derived from the Swe dish word trappa, signifying a stair. It would appear that this name was first used by Rinman, in a memoir on ferruginous stones, published in 1754. The Swedes applied this name to rocks, which, on exposure to the air, assumed shapes resembling the steps of a stair. It was, however, soon extended to a considerable variety of rocks of very different formations ; hence Werner found it necessary to restrict its signification. He un derstands by trap, rocks principally characterized by the presence of hornblende and black iron-clay. Hence all rocks occurring in the primitive class, having horn blende as a characteristic or predominating ingredient, belong to the Primitive Trap Formation.