5. Foreign Beds.—It contains more foreign beds than gneiss. The following have been observed : Granular limestone, dolomite, hornblende-slate, and hornblende rock, actynolite, garnet, talc, serpentine, chlorite, quartz rock, magnetic iron-stone, magnetic pyrites, copper pyrites, iron-pyrites, arsenic-pyrites, blonde, lead-glance, and cud ironstone.
6. Form of Mountains.—The acclivities of the moun tains are gentle, but the cliffs it forms are not so con siderable as those in gneiss mountains. When mural precipices occur, they ate seldom of great height. The summits of the hills are round backed.
7. Metallifirous Minerals —It is one of the most me talliferous of the mountain-rocks. The ores it contains occur frequently in beds, but more rarely in veins, which is directly the reverse of gneiss, where ores oc cur more frequently in veins than in beds. The ores that occur in beds are the following : magnetic iron stone, iron-pyrites, copper-pyrites, arsenic-pyrites, red iron ore, lead-glance, blcnde, gold, and glance-cobalt ; and these ores are accompanied with actynolite, garnet, and asbestus.
The veins that occur in mica-slate contain in general the same ores as those in gneiss.
The gold mines at the foot of Monte Rose are princi pally in mica-slate ; and this is also the case with some of those in the country of Salzburg. The silver mines of Johan-Georgenstadt and Braunsdof in Saxony ; those of Sweden and Norway are in these rocks. Many of the mines in Silesia and Bohemia are in mica-slate.
The most important mines in Sweden, as those of Dalecarlia and Fahlun; those of Roraas in Norway ; many in Hungary and Salzburg, Saxony and Bohemia, are situated in this rock.
8. It occurs in great abundance in Scotland ; as in the valley between Dunkeld and Blair-in-Athol ; the moun tain of Schihallion, and the neighbouring country ; island of Arran ; islands of Jura and Isla, Ste. It is also very widely distributed in the continent of Europe ; as in Saxony, Bohemia, Silesia, France, Spain, the Bannat, Transylvania, Switzerland, Salzburg. It also occurs in the United States, in South America, and in the conti nents of Africa and Asia.
IV. Clay-Slate.
Thonschiefer.— Werner.
Primitive Argillaceous Schistus, Kirwan Clay-Slate--Jameson.
Schiste argileux, Brochant. Phyllade.—Daubuisson.
1. Characters.—Clay-Slate is a simple mountain-rock, having a slaty structure, with a fine grained, and dull cross fracture ; it is opaque and soft, with a grey streak, whatever may be its colour. Its most frequent colours
are grey, or bluish black ; very often greenish-grey ; more rarely yellowish-grey and brownish-red. Oxide of iron is the general colouring ingredient; but in the black varieties it is carbon, which gives the tint of co lour. The greater number of varieties split easily into slates, which are either plain or variously convoluted. Their sou face is sometimes smooth, in other instances it is traversed by deep striae ; and it is sometimes dull, sometimes shining with a silky or pearly lustre. It is intimately connected with mica-slate, and there is a dis tinct tiansition from it into that rock, by the gradual disappearance of the quartz, thus skewing that it is en tire t% composed of m'ca in very minute and closely ag scales.
2. Var-tips.—There are four varieties of clay-slate. Thcfirsot kind has a yellowish-grey colour, and a shining lustre: it is the oldest kind, to use the language of Werner, and is that which reposes immediately on mica slate ; it is in short the link that connects clay-slate with mica-slate. The second kind is dark-grey; sometimes even bluish-grey and greyish-black, forming what is denominated roof-slate, From the circumstance of its splitting into thin and large tables. We must he care ful, however, not to consider all roof-slate as of primi tive formation. To this follows, in the order of succes sion, the third kind, which has a greenish-grey colour. The fourth and last, which is the newest kind of clay slate, is bluish-grey, and reddish : it contains a very few intermixed scales of mica ; possesses but little lustre ; and is the link that connects the primitive clay-slate with the transition clay-slate.
3. Strattfication.—It is distinctly stratified, and its slaty structure is generally parallel to the scams of the strata ; in some cases, however, a double cleavage is observable ; and Count de l3ournon observes, that many clay-slates break under angles of 60° and 120°, which he supposes may be owing to the presence of mica. The strata are in general much inclined, and are often variously convoluted and waved, and sometimes they appear to be composed of different concretions.