MRS. L.-Why these immense projections of the primary rocks, which in the low-lands lie concealed and covered beneath all the rest, appear thus unclothed and bare upon the heights, is not difficult to understand. They are the hardest and most enduring substances, capable of resisting the action of the elements to which these lofty regions stand exposed: if they were sometime covered, as probably they were, by the Secondary Rocks, those softer substances may have yielded to the winds and waters that assailed them, and been carried into the valleys, while the firmer Granite retains nearly its original position. Even of these mountains, however, the form has probably been changed by violence and worn down by time, and their elevation may sometime have been greater than it is. "Prodigious masses of Granite, detached most probably from their native rocks, are found among the Secondary Strata of the adjoining valleys; and the more distant they are found from the Granite Rocks, the more they seem worn and rounded. Of this description are the boulders or blocks of Granite observed by Sanpore on the east side of the lake of Geneva. One of these, called Pierre de Gonté, is ten feet high, with a horizontal section of 15 feet by 20. In the valley of Chamouny, several similar blocks have fallen from the Aiguilles. Some of these have been transported between thirty and forty miles; and as several mountains and vallies are now interposed, their transportation must have taken place at a very remote date. The celebrated foundation stone of the statue of Peter the Great, erected at St. Petersburg by Catherine II. is composed of a boulder or detached block of Granite, found in a bay of the gulf of Finland, whence it was transported to the capital; its length was 40 feet, its breadth 27 feet, its height 21 feet. In the isle of Arran, an immense block of Granite is found upon the shore, not only three miles from the nearest Granite rock, but having also a bay of the sea intervening; and several similar instances might be adduced, proving the great

ravages committed even upon so hard and unyielding a substance as Granite. We shall not then be surprised, that the same agents, acting upon softer materials, have made more successful depredations, and have in many instances completely denuded those granitic surfaces which were clothed by Secondary Strata."

MATILDA. I am impatient to be able to distinguish Granite when I see it, since it seems to make a very important part in the composition of our world.

MRS. L.-I will show you some specimens presently, and describe its more minute characters. Of its appearance in natural scenery a geological writer has remarked that "the aspect of a granite district in nature, is subject to variation: it however exhibits traits sufficiently peculiar, which are readily recognized by the traveller in his approach to it. In Cornwall, and in some parts of Ireland, especially in the county of Donegal, the granitic rocks are marked by the bold and abrupt precipices which they present to the attacks of the ocean; and by the barren and dreary aspect of the inland plains, that seem like immense fields, in which blocks of the stone have been torn from their beds, and indiscriminately scattered over the moss-grown surface. The elevation of these districts is not considerable-the granite is coarse grained, and splits into immense blocks, separated from each other by natural seams, and appearing like the ruins of edifices constructed by a giant race. In other cases granite forms irregular and broken peaks of prodigious elevation, and does not split into the blocks and masses just alluded to. This is the case in the Alps and Pyrenees; in the highest Scotch mountains; in the Hartz; and in the Tyrol. In Asia and Africa granite constitutes the Uralian, Altaian, and Himalayan chains, and the Atlas mountains; and in South America, the lofty ranges of Cordilleras are of a similar description." ANNE.-Is Granite the only Primitive rock-for I observe you speak of it exclusively.

MRS. L.-By no means-but it is the first, that is,

the lowest, and the most abundant. As existing below the surface, Granite is thus described-" Granite masses are sometimes continuous for a great space, so that they possess no definite form, or, if any such form be present, it cannot be discovered. At other times they are disposed in large bodies, not unaptly compared to feather beds, separated by fissures or joints. When these masses possess a large dimension in two directions only, they often resemble beds of stratified rocks, and have been mistaken for true strata. Occasionally these dimensions are so proportioned, that they resemble irregular spheroids: but these forms appear to have resulted from the wearing of the angles of masses originally prismatic. The extended beds above mentioned, are frequently subdivided by fissures into smaller prismatic and cuboidal masses; and as this subdivision generally takes place in two opposite directions, or are vertical and parallel to the great mass or bed, these prisms are found piled on each other in a manner resembling huge masonry, (Fig. 1.) The angles of the prisms being further subject to wear, as are the contiguous surfaces in a less degree, the result is an aggregate of irregular spheroids, often piled on each other in a very fantastical manner. This consequence, it is evident, can only take place when the fissures are nearly horizontal and vertical. In all others, the detached parts must fall away. A few rare instances occur in nature where the dimensions of the prisms are so considerable in one direction, that, when grouped in erect positions, they present an irregular columnar appearance. Lastly, the great laminæ or beds of granite are often vertical as well as horizontal or inclined; and it thus presents continuous smooth precipices laterally, while above it terminates in sharp peaks." (Fig. 2.)

MATILDA.-Keeping in mind our last conversation, I conclude you now speak of the External Structure of the Granite.

MRS. L.-Exactly; and we will thence proceed to

the Internal Structure, or Texture. "The Texture is, with one exception, always crystalline and confused, the several minerals of which it is composed, interfering with each other's forms. With the single exception of the graphic variety, it is also granular, but varying much in the fineness of the texture, or in the magnitude of the parts." In some specimens the texture of the Granite approaches so nearly to that of Porphyry, as to be difficult to distinguish from it-it is then called Porphyritic Granite-and we may be only able to decide which it is, by knowing where and under what circumstances it was found: but generally they are easily distinguished, as explained in our last conversation. "The magnitude of the parts in Granite is extremely various; each constituent mineral sometimes exceeding an inch in dimensions, and at others being almost invisibly minute. Various textures are often united in a very limited space, or the rock passes imperceptibly from fine to coarse grained. Occasionally also, irregular patches or veins of a fine texture are seen imbedded in a coarser variety.

ANNE.-It appears then that Granite is not a simple substance, but composed of several substances.

MRS. L.-"Granite consists fundamentally of Quartz, Felspar, Mica, and Hornblende, variously combined. These are not always present-sometimes the Mica is wanting, sometimes the Quartz-and occasionally other minerals enter into the composition, but being comparatively rare and not essential, I shall not notice them here.

MATILDA. But now I am in danger of being puzzled again, for I do not know what these substances

are.

MRS. L.-I will hereafter show them to you in separate masses-at present you may observe them combined in these pieces of Granite-changing its appearance according to their respective quantity, and making its colour almost infinitely various. "The Hornblende,

being invariably black or a very dark green, darkens the colour of the Rock-when in great excess, makes it almost black, in other cases of different shades of grey. Mica, when black, as it sometimes is, gives the same tints; but it is as often white or brown, and has then of course a different effect. The Felspar has a greater variety of colours than either of these, and being the most abundant ingredient of most Granites, chiefly determines the colour. Dark red and white are the extremes of colour in the Felspar, with all the intermediate shades of red, occasionally ochre yellow, grey, nearly black-in one rare instance green. The Quartz is most commonly white, or watery-but it may be grey, smoke coloured, or nearly black." Examine now these various specimens, and see if you can ascertain their component parts, or which substance prevails in them.

MATILDA.-Let us begin with Fig. 3-the grain is large-I can distinguish but three ingredients.

MRS. L.-It is the common, large-grained Granite. There is a Quartz of a dirty white-Felspar of a pale red, and a spot of black Mica at the corner.

ANNE. How do I know it is not Hornblende?

MRS. L.-Mica is a transparent, flakey, glassy substance, that cannot easily be mistaken, even in the combination of substances; though when black, it certainly approaches to Hornblende in appearance.

ANNE.Fig. - * is a small grained Granite. In this the Quartz and Felspar are both white-it seems to me that the Mica is white also, for I see some small transparent particles-the black specks I suppose are the Hornblende. But here is one quite different-there is something in it like coal, and much disposed to break in pieces when I touch it. Is this a Granite ? Fig. 4.

MRS. L.-It is a Granite of Quartz and Felspar, intermixed with a substance called Schorl, the black substance you speak of, and which you will hear of again,

N.B. From the accidental misplacing of the figures, this specimen is left unnumbered in the Plate.