Remarks tending to explain the Geological History of the Earth. By Professor ESMARK.*

IF we carry back our investigations with regard to the structure

of the earth to its original formation, we find all involved in thick darkness. There have not been wanting, however, ingenious men, who have formed theories on this subject; we find some of these even among the Greek philosophers. Among these, two opposite opinions especially prevailed; some considered fire as the chief agent in this process; others water. Anaxarchus from Lampascus averred, that in his country the mountains had stood under water. Aristotle, Eratosthenes, Strabo, and Plutarch, supported his opinion. In later times, nobody doubts this fact, as we find petrified animals on the highest mountains. In America, such have been found on the Andes, at the height of 12,000 Rhenish feet above the level of the sea †. At first it was believed that these petrifactions were remains of the general deluge; but a more accurate investigation discovered, that they could not all be derived from this source; for, as we find on the highest mountains, and inclosed in the bowels of the earth, petrifactions of animals in every stage of their growth, and arranged in classes such as we still find alive in the sea, it may be readily inferred, that the duration of the flood was not sufficient to produce that amazing multitude of organic forms, the remains of which are now to be found in the bosom of the earth, but that these places must have once been the bottom of the sea.

In considering these petrifactions with attention, we may observe the following peculiarities among them :

1. That the greater part of these petrifactions consist of sea animals and sea plants.

* It being our intention to lay before our readers, as occasion may offer, statements of the opinions on the formation of the Earth entertained by distinguished writers, we now communicate the ideas on this subject by Esmark, from the Christiania Journal.

the

+ Colonel Gerard found many ammonites at a height of 16,200 feet above sea, in the Himalya range of mountains.

2. That they are not all of the same sort.

3. That they have not all been deposited at the same time, but at periods far remote from one another.

4. That those which belong to the earliest periods have a less perfect organization, the farther back the less perfect; that those on the contrary which have been found in mountains of a later formation, have a more perfectly developed organization.

5. That we find a multitude of petrifactions of different animals which are now totally extinct, and that we find others which have some resemblance to animals now existing; but with differences which prove them to be of another species.

6. That we likewise find a great multitude of plants incorporated with the solid strata, of which some are different from those which now exist, while a great many seem to resemble them. The most remarkable circumstance connected with this fact is, that the climate of those places where these plants are found inclosed in the solid rocks, is not at all like the climate where they are now found growing. We find, for example, a multitude of plants in a state of petrifaction in the most northerly regions of Europe, which are now found growing in the torrid zone. As they are found with stalks and leaves, and sometimes even with fruit upon them, they must necessarily have grown in the places where they are now found, and could not have been wafted on the surface of the sea from regions lying far distant.

7. That of the human race, we find, with certainty, no remains inclosed in the earth, with the exception of a few which have been found partly in tuffaceous limestone, partly in clefts of older mountains which have since been filled up with sand, clay, and rubbish, and which must be considered as remains of the latest revolutionary changes in the earth.

We find a variety of theories formed in later times on this subject, by Burnet, Whiston, Woodward, Fontanelle, De Luc, Ray, Hutton, &c. They have each their own peculiar notions; and though it cannot be said that any one of them is right, this will be a matter of no surprise, when we consider how far behind they were in many of the sciences which have made such progress during the last century. Though from this progress in mineralogy, chemistry, physical, mathematical, and astronomical science, we stand on much higher ground than they did,

there is still much remaining which we cannot explain, with regard to the original formation of the earth, and the successive revolutions it has undergone, especially as we find that all these took place prior to the existence of the human race. For this reason, we are not able to give a perfectly satisfactory account of the history of the creation by Moses, who, without determining the length of this period, merely says, that, "in the beginning, God created the heaven and the earth, and that the earth was without form and void." In all probability a very long period, perhaps several thousands of our present years, intervened between the creation of the world and the time when the earth had advanced so far in the arrangement of its parts as to be capable of exhibiting signs of organization. By a day and a night, we now understand the period of the earth's revolution round its axis; by a year, the revolution of the earth in its orbit round the sun. Moses says, that the light was first formed, and that that was the first day. On the third day after this, the sun and moon were formed. As we have now no light but what comes either immediately from the sun himself, or by reflection from the moon; and as there was light, and likewise day and night before the sun and moon were formed, we must infer that the day here mentioned has been of a different character from our day, and that this light had a different source from an immediate communication from the sun. We may therefore conclude, that during the period of the incipient formation of the earth, it had possessed a light peculiar to its own constitution, such as we shall afterwards find exhibited in the case of other heavenly bodies in a similar stage of their formation.

For this purpose, let us cast a glance over the solar system, stating such phenomena as may assist in explaining this formation of the earth. On viewing this system, besides the earth, which completes its circuit round the sun in a period which we can exactly calculate, there are several other globes, some of them larger than the earth, and some of them smaller, which revolve round the sun likewise in a determined period, some of them longer than that of the earth, and some of them shorter. Besides these bodies, the planets, with their satellites or moons, there belong also to the solar system a multitude of comets.

There are several phenomena by which these last are distinguished from the planets. They revolve like them round the sun, but in much more eccentric orbits. The period of the revolution of a comet is very different from one century to another.* Their greatest distance from the sun is so immense, that if men could exist upon them, they would not see the sun for thousands of years, and the degree of cold must be such, that if there were sea or water upon them, it must be in a state of ice.

tance.

When these bodies are advancing to their perihelium, and at different distances approach nearer the earth, we observe that they are not only surrounded by a luminous atmosphere, but that they have likewise a long luminous tail, both of which become the greater the nearer they come to the sun, decreasing in the same manner as they remove from him to a greater disWith regard to this increase and decrease of light too, we observe a difference among them. In the case of some of them, almost the whole mass of the comet is changed into this luminous elastic atmosphere and tail; in others we perceive a distinct red nucleus, which, on its approach to the sun, has a less expanded atmosphere and tail. These atmospheres, and still more the tails, are so thin and elastic, that, without the least obstruction, we can see through them the lesser stars. Counsellor Huth has calculated, that the luminous matter in the tail of the great comet of 1811, was a million of times rarer than our atmosphere at the surface of the sea. The volume of its tail he computed to be 2000 times the bulk of the sun, and the diameter of its nucleus to be eighteen times that of the earth. Bessel calculates the period of its revolution to be 3383 years. Herschel has accurately observed this comet, and, among other things, he concludes, that its light was peculiar to itself. The colour of its nucleus was greenish, or a bluish green, and the nucleus or head was not in the centre of the atmosphere, which was most expanded on that side turned to the sun. The radius of the atmosphere he makes to be about 322,000 English miles, and the length of the tail more than 100 millions. By continued observations on this comet, he found that it underwent actual physical changes in its structure, and that it was globular. On

Their number is considered as exceeding 4000.

its approach to the sun, his light and heat seemed to produce chemical effects upon it; he believed that it revolved on its axis. By comparing this comet with that of 1807, he concludes, that every time comets approach their perihelium, they come nearer and nearer to the sun; that, therefore, the comet of 1807 had several times been in its perihelium, it beng 25 million of times nearer the sun than the comet of 1811. Its tail was only 9 millions of miles long, whereas that of 1811 was 91 millions. The effect of the sun on the latter was much greater than on the other, and it had probably seldom or never before been in its perihelium; whereas, on the contrary, the comet of 1807, in consequence of having been several times in its perihelium, must be more advanced in its growth, and matured. By comparing likewise the constitution of the great comet, with a smaller one in the same year 1811, he found that the smaller one was much more complete, and approached nearer the nature of a planet than the great comet, as the influence of the sun upon its perihelium, was not much greater than his influence on a planet in the same situation *.

I have made these remarks on the nature of comets, and this comparison of some of them, for the sake of introducing certain considerations, drawn from facts, which I consider as a proof that our earth, in its rude and undigested state, has been a comet. Of this hypothesis, I shall state, in what follows, several strong proofs in phenomena which occur in our own country.

Whiston, in his Theory of the Earth, supposes that it has originally been a comet, or the atmosphere of a comet, which, in its course round the sun, has moved in a very eccentric ellipse; that, of course, in its perihelium, it has been subjected to a very high degree of heat, and in its aphelium, to an equally strong degree of cold; that, in the one of these situations, it was vitrified by the heat, in the other covered with ice; that, by degrees, its orbit has gradually changed from this long ellipse, to that almost circular path in which it now moves on the whole, at a much smaller distance from the sun. How far does this agree with the phenomena which we can observe on our

See Phil. Transact. 1811, and Bode's Astronomisches Jahrbuch für das Yahr 1816, p. 185.