Urgebirge.— Werner.
Terrains Primitifs.—Daubuisson.
Primitive rocks are those whose period of formation is considered as antecedent to that of the creation of organic beings. Hence we arrange in this class all those formations which have not been found to contain petrifactions or fossil organic remains. Should future observations, however, prove that these rocks do occa sionally inclose animal or vegetable remains, still it would bd well to consider them as a distinct class, and retain the name primitive, because, from their lying un der the rocks of the other classes, they are to be consi dered as having been formed before them, and may, therefore, be said to be primitive, or first formed.
They are of chemical formation; and if mechanical deposites do occur associated with them, the quantity is inconsiderable. All those kinds which abound in mica are distinctly stratified, while the others that do not con tain it are less distinctly stratified. The direction of the strata is frequently parallel with that of the mountain range in which they are contained.
All the different rocks of the class alternate with and pass into each other.
The constituent parts are quartz, felspar, mica, lime stone, and hornblende, minerals indeed of which nearly the whole mass of the upper coat of the earth is com posed. Of these minerals, the felspar, quartz, mica and hornblende occur together, and in various forms of ag gregation, while the limestone forms beds of greater or less extent, which are but slightly intermixed or con nected with the boundary strata.
The following are the rocks of this class : 1. Granite, with sienite, protogine, and topaz-rock.
2. Gneiss, with some varieties of white stone.
3. Mica-slate, with different varieties of talc-slate.
4. Clay-slate, with alum-slate, flinty slate, Sec.
5. Granular limestone, and primitive gypsum.
6. Primitive trap.
7. Serpentine and euphotide.
8. Porphyry.
, 9. Quartz-rock.
I. Granite. Granite. !Verner.
.Saxum, quartz() spato scintillante et mica, in diversa proportione mixtis compositum.—Granites. Wallerius.
Granite of the Germans, French, &c.—Moorstone of
Cornwall. \Vhinstone and sandstone in some parts of Scotland.
1. The name granite is a corruption of the Latin word geranites, used by Pliny to designate a particular spe cies of stone. The first modern writer who uses this word is Torneforte, the celebrated naturalist. It oc curs in the Account of his Voyage to the Levant, pub lished in 1699. Antiquarians appear to have named every granular stone capable of being used in architec ture or statuary, granite, and it continued to be used in this vague sense by mineralogists until about fifty years ago, when true granite was distinguished as a particular mountain- rock.
2. It is a rock composed of grains or concretions of felspar, quartz, and mica, intimately joined together, but without any basis or ground. These parts vary in quantity, so that sometimes one, sometimes the other, and frequently two of them, predominate. Felspar is generally the predominating, as mica is the least consi derable, ingredient of the rock. In some varieties, the quartz is wanting, in others the mica, and these have received particular names. Such distinctions, however, are useless, as these masses are to be considered as mere varieties, not distinct species.
The constituent parts differ also considerably in their magnitude: they alternate from large to small, and even very fine granular. In some varieties, the concre tions of felspar and quartz are several inches in size, and the mica is in plates upwards of a foot square ; while in others, the grains are so small that the granite ap pears nearly compact.
It differs also considerably as to colour ; and this de pends principally on the predominating ingredient, the felspar, the quartz and mica having usually a grey co lour. The felspar is usually white, and most common ly greyish and yellowish bite; also reddish or milk white ; sometimes also flesh-red. It is seldom grey, yellow, or green. The quartz is usually grey, seldom milk-white, and always translucent. The mica is usu ally grey, and sometimes nearly black.