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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 Graníte. 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. VOL. V.
when I show you separately the substances you now see in combination. In this specimen you see the Schorl is a distinct crystal with six sides, dispersed through the Granite-base. This, therefore, would sometimes be called Porphyritic Granite-in Cornwall it is called Moor-stone. Here is one (Fig. 5), of a still finer grain than the former, in which the Felspar greatly predominates and decides the colour. You can here scarcely distinguish the parts--as far as I can perceive, it contains only wbite Quartz and Red Felspar. Thus you will find the colour and composition of Granite infinitely various - but the texture is still the same—an appearance of several substances crystalized together, in forms irregular and indistinct. Many other minerals, such as Garnets, &c. are occasionally found imbedded in the Granite, but seldom in such quantity as to influence its general appearance.
MATILDA.-I think I have now an idea of Granite, but I could not so readily distinguish its component parts -I should like to see them separately.
MRS. L.—This you shall do—but we cannot to-day prolong our conversation. There is a remarkable variety of Granite composed of Felspar and Quartz only, and so disposed as to have the appearance of written characters—whence it is called Graphic Granite. The probable origin of Granite we must speak of in a future conversation, Its uses you need not to be told. It is one of the most durable of natural productions, and on that account the fittest for building; but its extreme hardness is an objection in the working of it. Many parts of London are paved with Granite. In Dublin, there are some fine buildings constructed of it, of a beautiful kind found in the vicinity of the city. “In Wales, there is very little Granite--in the north of Scotland it is abundant-in England it occurs in Cornwall, Devon, Westmoreland, and Cumberland; and in small quantities in the Malvern Hills of Worcestershire, and Charnwood Forest in Leicestershire."
SERIES OF FAMILIAR CONVERSATIONS
ON THE ANIMAL KINGDOM.
CLASS ARTICULATA--SUB-CLASS INSECTS.
Insects in their Larva State. PAPA.--I am under a promise, I think, of giving you some account of insects and of the changes they undergo; and if you are disposed for it, we will devote this evening to the subject.
ANNA.—Thank you, Papa: I have been much wishing for it.
PAPA.-I believe I told you that all insects pass through four states : do you remember what they are ?
ANNA.-Yes, Papa; the egg, the caterpillar, the chrysalis, and the perfect insect.
PAPA.-Or, to speak scientifically, the egg, the larva, the pupa, and the imago. I am not fond of the peđantry of using scientific words, when those in common use would answer the purpose as well ;- but as we have no terms in our language that apply to the different states of all insects, it is more convenient, when we speak of them generally, to employ those which have been invented for the purpose.
ANNA._I suppose then caterpillars, maggots, and grubs, are all called larvæ.
PAPA.-Yes; the term larva is applied indifferently to all insects in their second, and pupa, in their third state: the words caterpillar, maggot, grub, &c., and chrysalis, nymph, semi-nymph, and cased nymph, definitely pointing out the particular sort of larva or pupa meant; just as in Botany, you know, the common term pericarp applies to all seed vessels, while the several kinds are designated by the names capsule, silicle, legume, berry, &c. Here is a cabbage caterpillar,
which will afford us an excellent specimen of insects in their second, or larva state.
ANNA.-What does the word larva mean, papa ?
PAPA.--It is a Latin word, signifying a mask. It was adopted by Linnæus, because the insect, such as it afterwards appears, lies as it were masked, or cealed, under this external form.
ANNA.-Do you mean to say, papa, that a butterfly lies concealed in this caterpillar?
PAPA.—Yes, my dear. It has been satisfactorily proved by Swammerdam and other naturalists, that the butterfly, with its organs indeed in an almost fluid state, but still perfect in all its parts, lies incased within the larva. Of this fact you might convince yourself by boiling a full-grown caterpillar for a few minutes, or by laying it for a few days in vinegar or spirits of wine, for the purpose of giving consistency to its parts: a very rough dissection would then enable you to discover the future butterfly. Its wings you would find rolled up into a sort of cord, and lodged between the first and second segment of the body; the antennæ and trunk coiled up in front of the head; and the legs, however different in form, actually sheathed in the present legs of the insect. But let us examine this caterpillar. You observe that the covering of the body is divided into a certain number of rings, which may be considered the skeleton of the animal, for it has no internal skeleton you know. These rings are united by bands of muscles; two lying on the upper, and two on the under side; by means of which it is enabled to bend its body in any direction, as you may perceive it is capable of doing. I believe I have already told you that insects are much more organized than any of the zoophytes: they have all not only muscles but nerves, which, instead of lying in the back, as they do in larger animals, are disposed in the under part of the body, that they may be secure from injury.
ANNA.—And they have a heart and veins too, have