where the summits are not volcanic, are either of granite or its modifications and associates. Now it is not impossible, and experience renders it probable, that these exposed peaks have once been covered, like their fellows in the lowlands, with some, or perhaps with the greater number, of the rocks which we have enumerated in the order of their superposition, but that these have yielded to the ruthless fingers of time and the elements; that they have been degraded and washed away, and that the denuded and indurated materials which they once covered, now stand the more durable, but still decaying, monuments of that former order of things; the valleys, we are told, are filled with the débris of the bordering hills, and the streams and rivers wash them into the ocean, and are gradually tending to reduce the surface of the earth to an unvaried plane. Lakes are filling up; bars are forming at the mouths of rivers; mud is gradually raising itself into dry land susceptible of cultivation, and the unfathomable depths of the ocean will one day or other become soundings, and ultimately, the waters of the sea will overwhelm the land, and man's dominion will be no longer suffered upon earth; or perhaps, to take the more cheering prospect, subterranean fires may again consolidate and elevate the detritus, and new islands and continents may arise out of the ruins of their predecessors.

Although these, and similar flighty hypotheses, deserve in themselves no serious consideration, they lead us naturally to inquire as to the cause of those irregularities which the surface of the earth exhibits the origin of hills and dales, of mountains and of valleys but let us first temper our minds for the consideration of this subject, by recollecting the extreme insignificance of these irregularities, and the paltryness of what we are regarding as most sublime and magnificent, compared with the bulk of our planet, to which they are but as particles of dust upon the surface of an artificial globe. In speaking of the transportation of granite boulders, I have already adverted to the probable non-existence, at the period of their lodgement in their present situations, of several of the deepest and most extensive valleys of the world; and if we examine the walls, as it were, of these valleys, or at

least of many of them, and observe that the same strata in the same position, constitute the hills that bound them, we shall have little reason to doubt that they have once been continuous, and that the intervening portion has been removed. Some cases of this kind have already been pointed out (see Vol. XIX. pp. 89— 90); but there are others yet more decided, and upon a much larger scale, as applying not to valleys only, but to the separation of islands and continents. Look, for instance, at the two sides of the English Channel, and the same strata, with the same peculiarities, are found upon its opposite shores: shall we then disbe lieve in the former continuity of these strata? Or when we discover the coast of Norway exhibiting the stratification of the Orkneys; Majorca composed of the same materials as Minorca ; the geological analogy of Corsica and Sardinia; that of the opposite shores of the Gulf of Venice, and many other analogous cases, shall we be inclined to doubt the removal of the once intervening matter? Shall we not read in these correspondences, the list of which might be much extended, the former non-existence of the intervening chasms, let them be valleys, or rivers, or arms of the ocean? and shall we not have disproved the original existence of, or contemporaneous formation of the valley, and may we not reasonably conclude, that as the irregularities of valleys depend upon the relative hardness and destructibility of the materials that form their sides, from the nature of their soil, from the direction of their ravines, and from some of the other facts that I have already observed upon, that water has been the great agent in effecting these excavations, and that certainly the mountainous protuberances of the globe are not the invariable effect of volcanoes; that valleys have not been formed by earthquakes; and that mountains are not accumulations of sand and of mud collected by submarine whirlpools, nor great crystalline shoots, as certain German and French geologists would insist.

But if we revert to the once even and regular state of the earth's surface, and admit that impetuous torrents of water have been chiefly concerned in carving out its irregularities, where are we to look for the origin of these torrents, or how are we to account for the gigantic effect which they have left behind?

Pallas ascribes them to the effect of earthquakes and volcanoes; some have insisted upon the agency and interference of a comet, and others have attempted to accommodate their speculations to the Mosaic history of the creation, and of the deluge, without having broached any particular opinion relative to the cause of the latter phenomenon; others again have dared to bring the credibility of scripture into the field of their discussions, and have elicited nothing but the contempt and disgust of the wise and virtuous part of mankind. Surely for all these purposes, the deluge is an efficient cause; and from the evidence already adduced, as well as from that which remains to be brought forward, it will be evident that to that source we must ascribe the principal inequalities and irregularities of our present surface.

We have now reviewed in succession the various strata which incrust the nucleus of our globe, commencing with the most superficial, and terminating with those which seem to constitute their foundation, and perhaps even the bulk of our planet. They present us with a series of records singularly interesting and eventful, and will already have appeared "as a book wherein men may read strange matters:" but their history is still imperfect, and I shall endeavour to complete the outline which I have sketched, by examining the contents of mineral dikes and metallic veins, by inquiring into the causes which tend to the disintegration and decay of rocks, and by stating the general effects of certain local agents, such as earthquakes and volcanoes.

ART. IV. Experiments on the Action of Water upon Glass, with some Observations on its slow Decomposition. By Mr. T. Griffiths.

[Communicated by the Author.]

It is a commonly received notion that glass is capable of resisting, to a very great extent, the attacks of active chemical solvents, and that its alkali can neither be readily separated nor exhibited in an insulated form without regularly submitting it to powerful decom

posing agents. Speaking of glass, in common language, without any reference to the many soluble compounds so designated, it may be a new fact in chemistry to prove that this singular substance possesses highly alkaline properties, which may easily be shewn by the usual tests.

Upon reducing some thick flint glass to a moderately fine powder in an earthenware mortar, for the purpose of analysis, a portion of it was placed on turmeric-paper, with the view of determining if it possessed any sensible alkaline property; and, upon being moistened with water, the yellow colour of the test-paper was instantly reddened nearly as powerfully as if lime had been employed.

This effect was considered as accidental, and as probably arising from some adventitious alkaline matter, or soap, adhering to the vessels employed. Another experiment was made, with greater care, in an agate mortar, but with the same, or even a more decided result, in consequence of the more minute division of the material. When pulverized on perfectly clean and polished surfaces of iron, steel, zinc, copper, silver, and platinum, the effect took place, and apparently with equal facility; but it was found that the presence of small quantities of oxide of iron greatly diminished it, in consequence, as was afterwards proved, of the particles of glass being by them defended from the contact of

water.

Since there are some saline bodies and metallic combinations which give indications of alkali to turmeric-paper, although perfectly neutral compounds, and as pure magnesia reddens this paper when moistened with water, although no solution can be shewn to take place, possibly this might be an effect of the kind, it scarcely appearing probable that any soluble matter should be abstracted from the powdered glass by the mere affusion of pure water. Litmus-paper, therefore, reddened by an acid, and paper stained with the blue infusion of cabbage, were also employed as tests; the former had its blue colour restored, and the latter was rendered green.

A portion of flint-glass in fine powder was boiled in water

for some hours; upon being allowed to cool, and subside, the clear portion was decanted and evaporated, and became strongly alkaline to the taste, and to other usual tests; a drop of its concentrated solution, gradually evaporated on a glass plate, on exposure to the atmosphere, in a short time became deliquescent. Tartaric acid produced an effervescence, and afterwards a precipitate in this solution; as likewise did muriate of platinum. From these experiments, therefore, it may be fairly inferred that the alkali removed from the glass was potash in an uncombined state, and that the alkaline effect observed in the first instance did not depend upon the presence of any alkaline salts, or combination, adhering to or diffused throughout the glass.

The remaining sediment from the above solution, after having been repeatedly washed in successive portions of water, became inert as to its action on test-papers, not affecting their colours in the slightest degree; but, upon trituration, its alkaline power was again developed; this property being evidently dependent upon the exposure of a new or undecomposed surface. A slight application of heat to the water, was found greatly to facilitate this evolution of alkali.

In order to determine the quantity of alkaline matter abstracted from a given weight of glass, by long and continued boiling, 100 grains of flint-glass, in fine powder, were boiled nearly every day for some weeks, in two or three successive portions of water; after this process, the insoluble residue was found deficient in weight by nearly 7 grains. This result, however, must not be considered as accurate, but as a mere approximation; for, on the one hand, small portions of glass might have been carried away in the supernatant liquor; and, on the other, more alkali might have been abstracted by repeatedly triturating during the process, which, under these circumstances, would be almost unlimited.

To some pure dilute muriatic acid was added very fine flintglass, in powder, till it was completely neutralized by its alkaline effect. Upon being allowed to subside, (which, however, was not very readily effected, minute particles remaining suspended for