except when it contains mica, to whose tabulated structure it then conforms. It often contains metallic treasures, as in Saxony, Silesia, and Sweden. It is pretty extensively distributed; existing very pure in Dalmatia, Greece, and the Archipelago. Paros was celebrated for its primitive white marble, in ancient times. Great excavations exist in its mountains, of which the celebrated grotto of Antiparos is an example.

Although we have described the order of the above primitive strata from below upwards, to be granite, gneiss, mica-slate, clay-slate, yet with the exception of granite, that order is often violated. The following are a few of the varieties presented by Dr. Macculloch in his Geological Classification of rocks.

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Granite, gneiss, limestone, quartz rock; in Glen Tilt. Granite, limestone, quartz rock, mica-schist, gneiss; in Glen Tilt. Hornblende schist also occurs in any part of this series.

Granite, clay slate with fine gray-wacke, gneiss; in Iona and Banffshire.

Granite, gneiss, primary sandstone-Sutherland. Granite, mica slate, secondary strata.

Clay-slate, gneiss, clay-slate. Islay and Rossshire.

5. PORPHYRY. This title comprehends a considerable variety of rocks, all of which present amidst a principal mass, crystals or crystalline grains distinct from it, but which are of contemporaneous formation. The basis or paste differs in its mineral nature, but is homogeneous to the eye, and the crystals which it principally contains are felspar.

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There is a considerable affinity between porphyry and granite; and the two rocks mutually pass into each other.

6. SIENITE, is a granite, in which the mica is commonly replaced by hornblende; with sometimes a little mica. It is named from Syene in Upper Egypt, where the ancients quarried it in immense blocks. The contrast of the white felspar and black hornblende gives it a pleasing aspect.

7. GREENSTONE, is similar to sienite, only the hornblende is usually in larger proportion.

From the very considerable inequalities in the primitive strata that cover the globe, we may conclude, that they could not be the result of a deposition from one primordial fluid, as Werner affirmed but that they were distributed originally in that order and form which the AUTHOR of Nature saw fit; so that like the integuments of animal and vegetable bodies, amid a general plan, there is that variety and choice which indicate the volition of intelligence. In our subsequent inquiries into the progressive changes developed on the crust of the globe, we shall perceive the same system of special design and adaptation.

We shall next proceed to advance evidence, in proof of granite, porphyry, sienite, and greenstone, the non-stratified and overlying rocks, being results of projective eruption; whence it may be inferred, that the mighty mountain erections of the earth, all intimately connected with these rocks, have been upheaved by internal force, when GOD bade the dry land appear, and hollowed out the ocean channels. And on this subject, I have the satisfaction to refer

to a faithful and sagacious practical geologist. I allude to Dr. Macculloch, whose researches among the primitive mountain façades of Scotland have enabled him to present a body of geological truths, worthy of entire confidence. The phenomena of Scotland, are not peculiar, but analogous to those observed by continental geologists.

The unstratified rocks are usually of a crystalline structure. They may be divided into two great classes; the one seated beneath, over, or among the primitive schists; the other lying above, or diffused between the medial and superior formations of a later epoch. The former appertain chiefly to the first period of creation, before organic bodies were formed; the latter belong to the whole interval between the creation and the present time.

8. GRANITE stands at the head of the first group of rocks. It consists of grains of felspar, quartz and mica immediately and intimately aggregated together. The felspar almost always predominates in the mixture; while the mica exists in least quantity. Yet nothing absolute can be pronounced concerning these proportions, as they are subject to great variations. Sometimes the mica diminishes, and eventually disappears in one portion of a granitic mass. The grains which compose this rock ought to be regarded as imperfect crystals, which have mutually interfered with each other, during their formation; the necessary space being wanting for their surface to assume their appropriate geometrical figures. They betray however, at times, their tendency to acquire these forms. Thus felspar occurs in granite as a regular four-sided, or six-sided prism;

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quartz as a double six-sided pyramid, and mica in a six-sided plate. In Siberia, mica is found occasionally in granites, in plates large enough to serve for window panes. On the other hand, the grains diminish sometimes in size, so as to be no longer discernible by the eye, constituting a homogeneous looking mass. The colour of the felspar determines the appearance of the rock; whence proceed red, gray, white, and other granites.

Quartz and felspar imperfectly crystallized, and influencing each others forms, produce an appearance of oriental manuscript. Such a stone is called graphic granite. This variety occurs exclusively in veins, particularly in those which traverse gneiss. The felspar is often greatly predominant. Quartz and hornblende combined, as well as felspar and hornblende, are found in granite localities, and therefore belong to the same rock, which distinguishes them from the greenstones of the trap family, or from basalt. These varieties occur in Aberdeenshire, where they are connected with common granite subjacent to gneiss, both by transition and alternation, circumstances decisive of their geological character. When distinct additional crystals of felspar are imbedded in the general mixture, porphyritic granite results, of which rock many remarkable examples are found in Cornwall. Quartz, felspar, and hornblende form a common mixture in some granitic localities of Scotland. To these, mica is occasionally added.

Mica and compact felspar, sometimes containing garnets, constitute white stone. Schorl and quartz

occasionally with felspar, compose the schorl rock of Cornwall, which belongs to the granite formation.

Serpentine may be here mentioned, as forming irregular masses included among the primary strata.

Under granites also we must include those veins which proceeding from them, traverse the adjoining rocks, together with those similar veins, which though of the same mineral composition, cannot be traced in the same manner to a fountain head.

Granite masses often extend over great spaces without any definite form; they resemble immense square beds, separated by fissures or joints, which the inexperienced have sometimes mistaken for strata. At other times the blocks are piled over one another in a huge masonry; with their angles worn by the weather. Such great blocks are sometimes seen standing on edge, with their summits peaked. Nothing of this kind can surpass in magnificence the gigantic spires of granite reared round the slopes of Mont Blanc.

Granite is one of the rocks most abundantly distributed over the surface of the globe, yielding in extent only to mica slate. In the Pyrenees, it forms on the northern slope, nearly from the summit, a band from one to four leagues broad, which constitutes in some measure the mineral axis of the chain. To the south-east of France, it composes with the other primitive formations, the greater part of the districts of the Vivarais, Dauphiny, Auvergne, Limosin, and a portion of Bourgogne. To the east, the Vosges are in some measure composed of it. In the Erzgebirge, in Saxony, it seems to