energy. Animals depend on plants, directly or indirectly, both for the food they eat and for the air they breathe. In the absence of sunlight plants would be unable to decompose the vast quantity of carbonic acid which animals breathe forth and thus their source of carbon and our source of oxygen would be cut off.

Another question must now be put and shortly answered. The sand and clay and chalk which form our cliff were laid down beneath the sea; how come they now to form dry land? Now it is clear that one of two things must have taken place: either the level of the sea has been depressed or that the land has been raised. Geologists do not hesitate to say that it is the land which has undergone the change in level, while the sea has remained stationary. The sea is, in fact, more stable, more constant, more ancient than our oldest continents. All land is, on the other hand, subject to changes of level. In the Himalaya mountains shells, which once lived in the sea, are found at an elevation of 16,000 feet above the level of the ocean. The northern part of Scandinavia is even now slowly rising, while the southern portion is undergoing depression. But how? There lies the question.

It is now well known that the Earth is, in the interior, in an intensely heated condition. In deep wells and mines the temperature rises about 1° Fah. for every sixty feet we descend. The melted lava poured forth during volcanic eruptions gives us some idea of the temperature comparatively near the surface. The centre of the Earth must then be hot beyond conception. But it is gradually cooling. Heat is flowing outwards through the crust into space: the cooling of the Earth is accompanied by contraction of the mass of the Earth and unequal contraction produces areas of depression and elevation.

Is this clear? Perhaps a comparison of great things with small will make it clearer. The human mind seems at times to fail to grasp facts which are, in truth, simple, but which from their magnitude are hard of conception. If, for instance, we stand on a high peak and look out over a portion of a great mountain chain, and see the grand summits standing out along the central ridge, it is difficult to conceive how this grand upheaval could have been produced; and perhaps the mind, wearied with the attempt to grapple with a subject almost too great for its powers, finds relief in the thought, that the mighty elevation was due to some great cataclysm or convulsion of Nature, concerning the cause of which--as a matter beyond our ken -it would be rash to speculate. And if it were then suggested that mountain chains, such as that in the midst of which we were standing, must be the inevitable result of the contraction of a cooling globe, it may be that our understanding would reject a conclusion which it could not at once grasp.

But if when we have left the mountain top, we take up a withered apple of last year's growth, the consideration of its surface may help us to understand that which before was so hard to comprehend. When we plucked that apple, a year ago, its surface was smooth, and the skin was stretched tightly over the fruit beneath. But since that

time the apple has shrunk in size, the fruit having contracted within the skin, which, no longer tight and glossy, is now wrinkled and puckered up.

:

But just as in the apple, so too in our planet, there is an inner portion which is contracting, and an outer portion which does not shrink and as surely as the earth is losing heat by radiation into space, her mass contracting and her size growing less, so surely must the outer portion become puckered up, the most prominent wrinkles forming what we call mountain ranges.

While sun-heat, therefore, enables rain, rivers, and the sea to denude the land and to combine in the formation of new continents, earth-heat causes a fresh supply of land to be raised above the waters. Were it not for this earth-heat England, as already mentioned, would during the course of geological time be entirely washed into the ocean of geological bankruptcy. All geological action, except that due to the tides, is brought about by sun-heat or by earth-heat.

Before inquiring what is the cause of this sun-heat and this earthheat, there is one more question to be answered. Of what does the air, the water, the cliff, ultimately consist? Are earth, air, and water, as the ancients believed, elements? No. The air is composed chiefly of a mixture of a gas called Nitrogen with one-fifth of its volume of Oxygen. It is not difficult, as will be seen in Professor Huxley's book, for the chemist in his laboratory to separate these two gases. Nor has he much difficulty in splitting up water into the two gases oxygen and hydrogen; while the further task of ascertaining of what the solid crust of the Earth is composed, though it requires more labour, is by no means beyond his powers. But whereas water contains but two elements, in the solid crust of the earth there are about sixty-five. But what are these elements? They are simple bodies which resist every effort of the chemist to decompose them into simpler bodies. Many chemists, however, believe that, though we cannot by any means at our disposal thus split them up, this is only because the means at our disposal are limited, and that, at an intensely high temperature, all would be found to consist of one primitive form of elementary matter.

One of the most striking results of modern scientific inquiry is the discovery, by means of the spectroscope, that there exists in the Sun's photosphere some sixteen or seventeen at least of the so-called elements, with which we are acquainted on the surface of our earth. Herein lies one of those many bonds, by which we are connected with our central luminary. The cause of these bonds; the origin of sun-heat and earth-heat; and of the Sun and the Earth themselves, now require elucidation.

According to the now-generally-accepted theory, known as the Nebular Hypothesis of Kant and Laplace (and it must be noted that we are here passing from the well known to the less known), our solar system was formed from a diffuse nebulous mass. We must imagine that this rotating spheroid mass once extended to the furthest limits of the solar system; beyond the orbit of Neptune. It radiated heat freely into space, and under the force of gravitation underwent

contraction. And as it contracted it left behind it rings of vapour which, breaking up, formed secondary rotating spheroids, themselves contracting, themselves leaving behind them rings, forming tertiary spheroids, themselves passing in their orbits round the central mass. That central spheroid mass is the Sun; one of the secondary rotating spheroids is the Earth, the Moon being a tertiary spheroid. The Earth-planet thus formed was gaseous; but as time rolled on, it passed through the liquid state, to the more or less solid state, which it at present possesses.

Sun-heat is therefore the result of the condensation of the primary spheroid earth-heat the remnant of that produced by the condensation of a secondary nebulous spheroid.

And now comes the question, how was the rotating nebulous spheroid formed?

If we take a small piece of lead and deal it a number of heavy blows with a hammer, we shall find that the lead becomes hot. If we continue to hammer for ten minutes, we shall find that the lead becomes too hot to hold. Now what is the cause of the heating of the lead. Simply this: when the lead is struck, the motion of the hammer is suddenly stopped: but the motion is taken up in a new form by the particles of the lead, and this new form of motion is heat. The visible motion of the hammer is converted into the invisible molecular motion of heat: for heat is simply the rapid vibration of the ultimate particles of matter.

When a bullet is shot from a rifle against an iron target, the rapidity of the motion is suddenly arrested; heat is developed; and this heat may in some cases be sufficient to melt the point of the bullet. In the same way the immense iron shot, hurled from our modern pieces of ordnance, cannot fail to be intensely heated, when they strike against the sides of such a ship as the Inflexible. It is quite conceivable that a shot or bullet of lead might be projected with such violence as to be, not only fused, but converted into vapour on striking the target. For when the motion of heat becomes extremely violent, the particles of matter are shaken asunder, and a vapour is formed.

We may take the velocity of a rifle bullet to be 225 feet in a second. The velocity at which the Earth moves through space, as she travels round the Sun, is about 19 miles in a second. If we imagine that the Earth were suddenly to strike a huge target, the heat generated would be sufficient, not only to fuse the Earth, but to reduce it in great part to vapour. "The amount of heat thus developed would be equal to that derived from the combustion of fourteen globes of coal, each equal to the Earth in magnitude. And if, after the stoppage of her motion, the Earth should fall into the Sun, as it assuredly would, the amount of heat generated by the blow would be equal to that developed by the combustion of 5600 worlds of solid carbon." Now, it is supposed by Dr. Croll and others (and here, be it noticed, we pass to the still less known: to the purely hypothetical, but still conceivable), that the nebulous mass from which the solar system has been evolved resulted from the collision in space of two

vast masses moving at great velocity. Each of these masses may be supposed to have developed from a nebulous mass, in the same way that the solar system has itself developed. Such nebulous masses were endowed with that high form of energy, which may be termed, generally, the energy of separation. But we have seen that this and all other intermediate forms of energy tend to run down, and be degraded to heat uniformly distributed throughout space. Some men of science tell us that this will be the ultimate condition of the energy of the universe. They tell us that the planets will fall into the Sun, and that thus the matter of the solar system will be aggregated into one mass: that this mass coming into collision with another mass similarly formed will produce the nebulous spheroid from which another system greater and grander than ours will be formed: and that so the same thing will go on until all the matter of the universe is aggregated into one mass, and all the energy of the universe is converted into uniformly diffused heat.

But here we have transcended the powers of the human intellect. We have reached that thin atmosphere in which we can no longer build. We have traced the chain of causation as far as we are able. We have reached the Unknowable. When we seek to go further: when we inquire what is matter, what is force, what is the ether through which force acts on matter, what is the space in which coexistences are manifested, and the time in which sequences are manifested when we inquire what is consciousness, what is the thought by which we are able to trace to some extent the chain of causation, we are met by alternative contradictories. We are in the presence of the Mystery of Mysteries. Let us humbly, modestly, truthfully confess our ignorance.

It may, perhaps, be said that there is much in the foregoing pages that is quite out of place in the GEOLOGICAL MAGAZINE much about wind and aqueous vapours, the Nebular Hypothesis and the Unknowable. But is it out of place? If there be any truth in my opening paragraph-that just as an artist has now and again to view his picture from a distance, so does the man of science have from time to time to take a comprehensive survey of his subject-No. In any consideration, however imperfect, of the work which Geology is doing for Modern Philosophy, we must weave that work into the general picture presented by the study of Nature. This I have attempted to do. In the first place I have endeavoured to point out the law of causation; that all that we see about us has been caused in some way or other. In most cases, from the nature of the subject, this law of causation has been illustrated qualitatively: but in the case of the formation of water-vapour the quantitative truth of the law has been indicated; and the law of the conservation of energy briefly alluded to. In the second place I have tried to show, as far as was possible in the space at my command, how the crust of the Earth has been built up by the mechanical agency of rivers, forming deltas, and the vital agency of simply-constituted creatures. By these two agencies nearly all the rocks have been formed, with the exception of salt, and, perhaps, magnesian limestone, which are due to

chemical agency. By the action of earth-heat and other causes, however, some of these rocks have been so altered that their original source is scarcely, if at all, recognizable. How this earth-heat has raised the strata, thus formed beneath the sea, above the waters of the ocean, has been pointed out; and the action of the sea-waves, and of rain and rivers in carving out the face of the country, horizontally and vertically, has been indicated. In tracing the chain of causation from the well-known to the Unknowable, I have not followed the example set by Prof. Huxley in the excellent little book which bears the same title as this article. In these days, however, when we hear so much of the "pride of Science," it is well to point out that in the study of Nature we reach at last ultimate questions, with respect to which we must one and all confess with modest humility that we are and must be ignorant. Finally, in making each fact the effect of one which had gone before it, in time, and the cause of one which followed, I have aimed at that organization of knowledge, without which any number of accumulated facts are but isolated pieces of general information.

II. ON THE NOMENCLATURE OF SAUROCEPHALUS LANCIFORMIS OF THE BRITISH CRETACEOUS DEPOSITS: WITH DESCRIPTION OF A NEW SPECIES (S. WOODWARDII).

D

By WILLIAM DAVIES, F.G.S.,

of the British Museum.

(PLATE VIII.)

R. MANTELL, in his classical work, the "Fossils of the South Downs," figured two large compressed and lanciform teeth' preserved in his collection and obtained from the Chalk at Lewes, as respectively the teeth, of an unknown fish and of a species of Squalus. Similar teeth, and from the same collection, were subsequently figured and described by Prof. Louis Agassiz, who, from external characters chiefly, considered them to have belonged to a Sphyrænoid fish, and he referred them to an American species founded by Dr. Harlan upon portions of jaws with teeth in situ found in a Cretaceous deposit in the State of New Jersey, but described by him as remains of a Saurian, and to which he gave the name of Saurocephalus lanciformis. At the time when Agassiz referred these teeth to Harlan's species, and determined their ichthyic character, he had not seen the American fossils; but he states that these conclusions were subsequently confirmed by Prof. Owen's description and drawings of the microscopic structure, and of teeth of the natural size of the Saurocephalus lanciformis, Harl., in his "Odontography," p. 130, pl. 55. But Prof. Owen's researches were made upon a genuine tooth of the American fossil sent to him by Dr. Harlan, and not upon an English specimen. For some years after the publication of Agassiz's work the species 1 op. cit. pl. 33, figs. 7 and 9.

2 Recherches Poissons Fossiles, tom. v. p. 102, pl. 25 c, figs. 21-29.

3 Journ. Acad. Nat. Sc., vol. iii. p. 337, pl. xii. figs. 1-5.