part of the earth has been formed. I shall not bring forward all the observations necessary in a complete system, but only such as are most intimately connected with the proposition under consideration; and I shall in general, and as much as I can, confine myself to new data; observing, in the mean time, that all the old and well established facts fall in with these data in such a way as to lead as near as possible to a true theory.

Some geologists arrange all the known matter of the earth under the classes primitive and secondary; others make the divisions primary and secondary; and others divide into primitive, transition, and floetz. None of these classifications is sufficiently correct. The term primitive probably originated from the idea that the matter so called is in its original solid state; and if this word were not applicable to matter arranged in the other classes, and had no reference, in contradistinction, to the term secondary, it would certainly in this sense be applied with propriety; but when, considered with reference to the word secondary, its aptness is altogether lost; for though secondary matter is not in its original situation, it undoubtedly possesses its first state of solidity. In other respects these terms are improper: the greatest part of primitive matter is unstratified, but some varieties are stratified, as, for instance, quartzy sand-stone, or stratified quartz, compact green-stone, &c. Now as primitive matter is both stratified and unstratified, the distinction is lost, and the matter of two classes confounded together. These objections apply with equal force to that arrangement which divides the earth's matter into the primitive, transition, and floetz classes. To these objections may be urged those which follow. All the matter belonging to the classes primitive and transition is strictly primitive; therefore if a distinction be made in classing this matter, it ought only to be of subordinate consideration. If the term floetz literally means stratified, it is sufficiently distinct, provided no matter is arranged under it that is not stratified; at any rate, however, stratified is by much the better term. But whatever be the opinions of geologists as to the earth's mode of formation, two terms, namely, concrete and concrete-stratified, may be used, which accord exactly with its structure, and which have very little reference to theoretical speculations.

Of Concrete Matter.

The concrete matter comprehends the primitive or primary matter; and includes all the primitive; some, if not all, of the transition; and a few of the floetz, and the newest floetz trap formations of Werner. This matter may be divided into earth-stone and lime-stone.

The earth-stone completely surrounds the inner part of the earth. It is a concrete mass that can only be distinguished inte

parts which differ from one another in appearance; and the essentially differing parts are arranged into completely concentric layers. That the concrete earthy matter is a great and universally continuous mass, I will now endeavour to show. The visible parts of this matter are generally situated on the highest parts of the dry land; on a lower level, the concrete lime-stone puts on; and below it the stratified matter commences. Were we to draw a sectional line through a large visible part of this matter, in any direction except the longitudinal one, the centre of the part would be the highest point, and from this place the line would bend downwards in a regular and easy curve, till either the lime-stone or the stratified formations were met with; and if the former, the line would still descend, but easier than before, till it reached the stratified formations; it would then incline a little, but would be nearly horizontal if we pursued this line straight forward, it would ascend easily the contrary way, while it passed through the stratified ground; then steeper over the concreted lime-stone; and still steeper over the concrete earthy matter, to the summit of the ground. After observing this line again descend for a certain distance, it would re-ascend; thus passing over a visible portion of earth-stone; then over the lime-stone, or the stratified formations, or both; and then over another part of the earth-stone; and so on alternately. When we observe the curve of the earth-stone, and examine how the lime-stone and stratified matter put on, we at once give the negative to the idea that the earth-stone terminates where the lime-stone or stratified matter commences, and conclude that it continues under them; and as a proof that this conclusion is just, we actually find some of the earth-stone's great eminences reaching above them. Again, when we have traced the descending part of a series of stratified formations, and meet with another elevated part of the earth-stone, it appears as if it rose from under the stratified formations near it; in other words, its surface inclines to the other portion in such a way as to show that these portions are only the visible parts of the same mass. Hence we may infer that the earth-stone is an universally continuous mass that exists every where in low as well as in high situations; of course it envelopes the inner part of the earth, and contains in its surface-hollows the lime-stone and stratified matter.

The earth-stone is divisible into parts which differ in external characters. Such parts, however, are firmly united together. The parts that differ essentially from one another are arranged in concentric layers. There are two layers exposed at the surface, and found in mines. The lower layer is granulated, or grained, and consists of granite, sienite, &c.; the upper layer is compact, and is composed of clay-slate, mica-slate, &c. The concentric arrangement of these layers will be evident from what follows. In every extensive part of the earth-stone we find at least one variety of grained earth-stone. Now if we make observations on. the shape

and relative situation of such parts of the grained earth-stone, it becomes evident that they are the visible parts of a concentric layer which underlies, but is united to, the compact layers. Let us instance the primitive district in Cornwall and Devonshire. If a person views the section of the largest granite hill near Redruth, taken in a straight line towards Dartmoor, in this direction the surface of the granite descends regularly till covered with the compact layer; then this layer descends also in the same direction, for a certain distance, but not so steep as the grained layer, or granite. Let this person now remove himself to Dartmoor, and take a sectional view of this hill in a straight line to the granitic hill near Redruth. The Dartmoor granite descends towards Redruth precisely in the same way as the Redruth granite does to Dartmoor, till it is covered by the compact layer; which also declines to the place where it dips to from Redruth. Now the inference is, that these are two of the highest parts of a granitic layer which lies totally under the compact layer in this part of the country; and the fact is, that the granite and granitic veins, which proceed from it, are found in the intermediate space between Redruth and Dartmoor. The same conclusions may be drawn if a person looks towards the granite near the Land's End, or towards the Bristol or British Channels. Hence these granitic masses are but the visible parts of a grained layer that lies under the compact layer in this part of the world. Now as all granite or other grained parts present the same appearance as these, and exist in every elevated part of the earthstone, the grained layer which is found in Cornwall is but a part of such a layer that continues in every direction round the world, and appears in every country, in consequence of having an undulating surface, whose eminences reach above the compact layer. Finally, specimens of the different varieties of grained earth-stone, such as granite and sienite, approach so near one another in appearance, that it requires the most expert mineralogist to determine with precision to which variety some of them belong. There, therefore, appears to be no difficulty in the way in supposing that granite and sienite are portions of the same mass; on the contrary, this deduction might have been drawn from their approximating appearances.

The undulated surface of the earth-stone was produced in the following manner. The process of consolidation proceeded upwards from below till it reached the earth's surface. Before it had acted on the grained layer, a number of inequalities commenced in the surface, which divided the solid from the fluid matter, because the matter below contracted more, and in consequence sunk lower in one place than in another; as the consolidation continued upwards, these inequalities increased, and at the surface gave rise to the undulations which I have described, when speaking of the earth's features, as being peculiar to primitive districts, and also produced such undulations as contain a series of stratified formations in their lower parts. The hollow between the top of Keswick Mountains,

and the top of those in the Isle of Man, is the lower part of one of the last-mentioned undulations. There would be a time when the undulations in the surface between the solid and fluid matter were so great, that the latter matter would retire into hollows, and stand just as high as the highest parts of the former matter. In the continuation of the process, the elevated parts of the solid earth-stone would gradually extend above the surface of the earth-stone's fluid matter; because the hollows in the surface of the solid matter would increase in size, and the still fluid matter retire into them. In this way the fluid portions of the compact layer got below the higher parts of the grained layer; and till the consolidating process reached the general surface of the compact layer, the fluid matter kept sinking, and its surface retiring downwards, and leaving a part of this layer solid and united to the grained layer; but when nearly the whole of the compact layer had obtained the solid form, its surface assumed throughout a series of small undulations, whose dimensions continued to increase till the matter had reached its present degree of solidity.

2. Of Concrete Lime-stone.

This matter comprehends all those grained and compact limestones and chalk which are not stratified; and includes most of the primitive, transition, and floetz, lime-stone and chalk, formations of Werner.

The matter of the lime-stone while in a fluid state completely covered the earth-stone. When the compact layer had assumed the solid form, the consolidation of the lime-stone layer commenced. But previous to this event the fluid calcareous matter had first sunk gradually below the tops of the grained layer, and then below the higher parts of the compact layer. As the inequalities in the surface. of the earth-stone are very great, the universal continuity of the lime-stone was destroyed, and parts of it, while still fluid, were kept back in hollows; and parts arrested by the consolidating process as they were retiring downwards. It is, therefore, found either bending round hollows of the earth-stone, or only lying in parts on one of the sides of such hollows. We are now come nearly to the conclusion. Had there been no inequality in the contraction of the earth's matter after it had assumed the solid state, the grained and compact earth-stone layers, and the lime-stone layer, would have been completely hid by a stratum of water equal in quantity to the present ocean, which last may be considered the remains of that fluid from which the lime-stone proceeded; by the same rule the stratified formations could not have existed. But as the unequal sinking produced hollows, and exposed the earth-stone and lime-stone to view, and as the ocean retired into, and was again forced out of, these hollows to its present situation, by the slow and progressive accumulation of stratified formations, this unequal sinking of course gave rise to a variety of formations. Now

"

as the unequal sinking is a consequence of the unequal contraction, the phenomenon of formations must be a consequence of the unequal contraction of the earth's matter."

Having now finished what I proposed, I will close these essays with some general remarks on stratified formations. I consider the great formations, namely, the sand-stones and coal formations, to be formed in the manner that lakes are at present filling up. The sand-stones are large bars deposited by former rivers at the places where they entered former lakes, and the coal formations are the sediments of these lakes.

I scarcely need remark how well the position, relative situation, and the nature of these formations, accord with this idea; nor need I show with what facility this theory at large accounts for the existence of entombed marine animals so high above the present ocean; nor why these bodies are in general confined to lime-stone, the large vegetables to the sand-stone, and the small to the coal formations; as these phenomena admit of the easiest and clearest explanation upon the principles displayed in these essays.

ARTICLE XI.

Extract of a Letter from Mr. Benedict Prevost, Professor at Montauban, to Mr. Pierre Prevost, Professor at Geneva, respecting the Dew which is deposited on that Side of Panes of Glass where the Air is coldest.

THE annexed abstract of a letter from Mr. B. Prevost relates to a fact which has been discussed in your Journal (vol. vi. p. 379, 432).* I think your readers will consider it as necessary to complete the discussion in question.

(Signed)

Geneva, Jan. 1816,

I am, &c.

As to the humidity which is deposited on the outside of a glass pane, though the air on the outside be colder than that within, I am certain that I have observed it several times, pretty frequently indeed. I mean that I have observed this humidity on the outside when the external thermometer was lower than the internal. But you know, my dear cousin, and you state it yourself (at No. 24 of your § 192, p. 241), that I endeavoured to procure thermometers with flattened bulbs, and sufficiently sensible to point out the diffe