getation. The four great periods are as follows: A.-The First Period includes the C.-The Third Period commences D.-The Fourth Period includes all the strata more recent than the chalk. (C to F.) It is a remarbable circumstance that the periods are separated by strata, which, if not entirely destitute of land plants, contain them in very small quantity. Thus A is separated from B by a formation of coarse sandstone (called by geologists the red conglomerate), in which plants are of rare occurrence, and by the magnesian limestone in which marine plants are almost exclusively found again, B and C are separated by the shelly limestone (muschelkalk of geologists), which is almost destitute of vegetable remains: and, lastly, C is separated from D by the chalk; in which, with rare exceptions, only marine plants have yet been found. FIRST PERIOD. The lowest strata in which animal remains are found contain also those of plants, so that it would appear that animal and vegetable life were from the first co-existent. The plants in the older sandstones are for the most part marine, but the impressions are usually indistinct. Black carbonaceous matter, without any organic form, is by no means unfrequent, and sometimes in considerable quantity, and it is not improbable that it is of vegetable origin, for fossil plants are very commonly found in the state of charcoal. It is in the beds of coal, and in the sandstones, clays, and limestones which accompany them, that vegetable remains first occur in profusion, and there are few phenomena in geology more remarkable than those enormous accumulations of vegetable matter from which the coal-beds have been derived. The most distinguishing feature of it is the great numerical preponderance of the third class-viz., the vascular cryptogamæ, and the prodigious size which the plants attain. They constitute fivesixths of the whole flora of the period, while they do not form the proportion of one-thirtieth in the vegetation of the present time. The ferns of temperate regions are low plants with stems rising scarcely a few inches above the ground, but in the equatorial regions there are what are called tree-ferns, which have a stem from twenty to thirty feet high. Now the different kinds of fossil ferns of this period often correspond with the tree-ferns of the tropics, as is attested by the remains of their stems, which are occasionally met with. The plants called lycopodiums by botanists constitute another order of this class, and are of a kind intermediate between tree-ferns and the fir-tree tribe. Those now existing never exceed the height of three feet, and are usually weak prostrate plants, having the habits of mosses; but the fossil lycopodiums attain gigantic sizes, stems having been found above three feet in diameter, and seventy feet long. There is in this period a much smaller proportion of the fourth and fifth classes, in comparison with what occurs in existing vegetation; and, with the exception of the fir tribe, which was very common, the existence of the dicotyledonous class is little more than conjectured. plants which constitute by far the larger proportion of the flora of the first period belong to genera which exist, of such dimensions, only in the warmest countries of the globe; and it is evident, therefore, that the climate of the north of Europe and America must have been at least as hot as that of the equatorial regions, at the time the plants grew which are now buried many fathoms under ground in the coal-mines of those countries, for all the circumstances attending them exclude the idea of the plants having been drifted from southern latitudes into those situations. The Second Period. The red sandstones which were deposited so extensively at this period are even more destitute of A vegetable than they are of animal remains. This absence of organic remains is a very remarkable and inexplicable circumstance, considering the great extent occupied by these deposits in all countries, and their vast thickness. The plants hitherto found in the lowest strata of the period have been almost exclusively marine, the few exceptions being vascular cryptogama, resembling those of the first period. In the superior beds, a few of the coniferæ or fir-tree tribe have been found, and some that are supposed to belong to the monocotyledonous class. Third Period.-The lowest stratum of this period contains very few plants, and these chiefly marine; but they become more abundant in the sands, sandstones, clays, and limestones that succeed each other in numerous alternations up to the chalk. Many belong, however, to an entirely new race of plants from any which had previously existed. There are no longer the gigantic ferns and lycopodiums of the first period,—the same families exist, but the character of excessive luxuriance disappears, and species analogous to plants-now natives of the Cape of Good Hope and New Holland-become common. The whole of the flora of the period consists almost exclusively of the third and fourth classes, and nearly in equal proportions: the rarity of the fifth and sixth classes, that is, of monocotyledonous and dicotyledonous plants, is very remarkable. Among those belonging to the fourth class, viz. the gymnospermous phanerogamæ, there is an extraordinary preponderance of the family called cycadeæ, a family scarcely so numerous now over the whole globe as it was then in the small part of Europe where its fossil remains have been found: it constitutes now not above a thousandth part of existing vegetation, whereas it forms one-half of what remains of the flora of this period. The chalk, which constitutes the upper strata of the period, has not afforded as yet more than a few marine plants, and scarcely a trace of land plants, so that a complete change had taken place in the nature of the country surrounding those parts where the chalk was deposited, from what had existed immediately before. Fourth Period.-From the termination of the deposit of the chalk formation, we discover in the animal and vegetable remains the commencement of resemblances to species which now exist; the proportion gradually increases in the newer strata, until, at last, the flora of the latest tertiary deposits differs very little in character from that of the present time in the same countries. In the beds immediately above the chalk, ferns and cycadeæ again appear, but in greatly diminished proportions; the coniferæ, but very different from those of the older periods, increase in quantity, mixed with palm-trees and others of the monocotyledonous class of tropical regions, associated with dicotyledonous trees, such as the elm, willow, poplar, chestnut, and sycamore. We again meet with local deposits of decayed, or rather altered, vegetable matter, forming thick beds of a kind of coal, which is used in many countries, as on the banks of the Rhine, for fuel,- something intermediate between coal and peat. This geological sketch has extended to a much greater length than we originally intended. We have endeavoured to compress it as much as possible, and are apprehensive that the subject may still appear to some readers very obscure in many important points. In this sketch we lay no claim to originality: it is, on the contrary, simply a compilation from a popular treatise on geology, which appeared some time ago in the Penny Magazine, from the pen of an eminent geologist, but is only therefore the more deserving of respect, as the statements and the reasonings which it contains were not written with a view to support or coincide with this theory, and cannot be suspected of leaning towards it with an undue bias. Those who may wish for fuller information are referred to the works of Baron Cuvier, "Lyell's Principles of Geology," and an excellent work on the geology of England and Wales, by Phillips and Conybeare. We will now conclude with a short review of the principal facts and conclu.. sions to which geologists have arrived, and compare them with the leading principles of our theory. 1. Age of the World.-We learn from geology, that, prior to the creation of man, the earth had existed, and had been covered with innumerable species of living beings, for a long series of ages; to which we are unable, and, pro bably, shall ever remain unable, to fix any definite limits.-This agrees with our theory. 2. Change of Temperature.-We also learn, that, during the deposition of the inferior beds of the secondary strata, the climate of the north of Europe was many degrees hotter than the West Indies. Specimens of rocks have been brought from Melville Island, the remote northern land discovered in the late polar expeditions, some of which contain, imbedded in the stone, portions of plants belonging to an order now known only to exist in the warmest parts of the equatorial regions. This we attribute to the decreasing activity of the galvanic circle flowing through the earth's external crust. We know that, by the action of the galvanic circle, heat is evolved in proportion to the intensity of the action; that, when very intense, it will melt the most refractory substances, and that it exhausts itself in a ratio corresponding with the degree of its intensity. Upon this principle we hold that Uranus is from his innate heat the warmest of all the known planets, and that, in that respect, Mercury is probably the coldest. 3. Inclination of the Stratified Rocks. —Geologists refer to volcanic action to account for the inclination of the strata ; and it must be admitted, that, in some cases, this accounts for the appearances very satisfactorily, but in a great majority of instances it is found that the lower members of the stratified rocks have not been disturbed from their horizontality to the same extent as the superior strata: the lower members are often found on a levél foundation, the strata lying immediately upon them being in a highly-inclined state. Now it is evident, that, if volcanic action had been the cause of the inclination, it could not have disturbed the superior strata, leaving the inferior beds undisturbed, seeing that the lower strata are nearest to the supposed disturbing force. Some other mode of accounting for these appearances must therefore be discovered. A natural section of the stratified rocks often presents to the mind the appearance of immense fragments of extraneous matter, scattered upon the surface of the earth, having fallen in every possible form and position. This view of the case receives consi derable support from the oblate figure of the earth it is computed that the earth's diameter is twenty-seven miles less from pole to pole, than if measured through the equator; a considerable portion of this excess in the equatorial diameter is, according to our hypothesis, to be ascribed to the depositions of the several satellites that have been at different periods scattered upon the earth's surface. This may easily be conceived, if it be considered that any adventitious substance, scattered upon the surface, would be naturally drawn towards the equator by the earth's rotary motion. It is also extremely probable the orbits of the satellites and the earth's equator were nearly coincident, which may further account for the great excess in the equatorial diameter, as under these circumstances the deposition of the satellite must necessarily have taken place within the tropics. And, further, this view will be very much strengthened, if we take into our consideration that nearly all the ranges of very lofty mountains are within or near the tropics; that they decrease in altitude as we recede from the equator, and that near the poles there are no elevations of any magnitude. 4. Derivation of the Secondary and Tertiary Rocks.- Geologists consider that the primary strata enveloped the earth somewhat like the coats of an onion that this envelope was broken and elevated by a force acting from beneath; and that in the valleys and hollows thus formed the secondary strata were deposited; the matter necessary for their formation being derived from the elevated parts of the primary strata, and that in this manner all the strata have been deposited; elevations and depressions of the strata sometimes intervening between the several depositions. We have only one remark to make upon this, with which we will conclude our geological observations. The secondary and tertiary strata contain rocks of a totally different character, as regards their mineral composition, from any that have been observed among the primary rocks; it is, therefore, evident that the whole of the secondary rocks could not have been derived from the primary, seeing that the former contain matter which is not to be found in the latter. Before we conclude, we would direct the attention to a very remarkable inequality in the moon's motions, called by astronomers her secular acceleration. As this article has already extended' to so great a length, we shall make no comment upon it, but leave the reader to draw his own conclusions. It appears, that "it is to Halley that we owe the first suspicion of this very important fact regarding the moon's motions. It had been hitherto the universally received doctrine that all the planets, without exception, were subject to such inequalities only as are renewed within a certain space of the time, and which, on that account, have been called periodic inequalities. The mean motion is determined by a comparison of the planets' places, at very distant times embracing a great number of the periods, within which the inequalities are renewed, so that the result obtained is quite independent of these inequalities. No astronomer had ever ventured to doubt the uniformity of these mean motions; and, in fact, we now know that the major axis, and, consequently, the periodic times of the primary planets, are not subject to any but the periodical inequalities of which we have spoken. But this is not the case with the moon. The mean motion of that satellite is continually accelerated; and as this acceleration, though, mathematically speaking, it has a limit, yet will continue for perhaps many thousands of centuries, it is called the secular acceleration, to distinguish it from those inequalities which have a period that falls within the limits of observation. The cause of this phenomenon was discovered by Laplace; the fact itself was first suspected by Halley. The reality of it was disputed for a long time, but it is now incontestably established. The mean motion of the moon, as determined by modern observations exclusively, is between three and four minutes more rapid than that found by comparing modern observations with the eclipses observed at Babylon 700 years before Christ; and this result is fully confirmed by two eclipses of the sun, and an eclipse of the moon, observed at Cairo, by Ibn Jounis, towards the end of the tenth century:"* We presume that the geometrical demonstrations of the Newtonian philosophy History of Astronomy of the Library of Useful Knowledge, p. 80. will not be effected by this theory. Whe ther we ascribe the effects to the agency of electricity, a power of whose existence we are assured by the evidence of the senses; or whether we refer them to gravitation, a conventional term adopted for the purpose of explaining a certain effect resulting from no known cause. If each of the powers be allowed equal to the observed effects, the demonstrations cannot be affected by a mere change of terms. We ought never, at any time, to rest satisfied with the present state of knowledge, or conceive that all the mys teries and laws of nature have been un-folded and expounded. There are many important principles yet to discover, of which we little dream at present, for, as has been truly and beautifully observed by a modern writer, "Between the ultimate point of discovery, and the place we now occupy on the ascent towards it, the steps are so inconceivably many, that, with regard to us, they may be most truly described as interminable. So far as we have experience or can conceive of knowledge, it is an expanse ever widening before us and around us. Its horizon seems not only always as distant as ever, but always becoming more distant the more we strive to approach it. For every one discovery is merely the opening of a road to other discoveries, and the lifting of us, at the same time, to a new eminence, from which we see a broader domain than before, both of the known and of the unknown." We will here take our leave of this subject for the present, recommending it to the attention of your scientific readers and correspondents. There appears to our mind such a universal consent and agreement in all the different parts of this hypothesis, that the conclusion is forced upon us, that it will at some future time be received as the true system of the universe. T. S. M. THE BRITISH MUSEUM. Sir,-As a Committee of the House of Commons has lately been appointed to continue the inquiry of last Session into the affairs of the British Museum, it is to be hoped that some regulations will be made respecting the opening of the house on Good Friday, and in the Easter, Whitsuntide, and Christmas holidays. There are thousands of persons who re unable to visit this establishment at any other time, and why should they be excluded from this agreeable recreation and instructive promenade? It is objected by the Principal Librarian, in his evidence (No. 1,319), that the Museum must be thoroughly washed and cleansed in these three weeks, that the house may "smell wholesome," and that the "fleas" (No. 256) may not inconvenience the readers!!! But why select these identical weeks for this purpose? Why not close the Museum in the week after the Easter, Whitsun, and Christmas. weeks respectively, if such extensive purgations be necessary? But with six or seven housemaids, might it not be cleansed every day before breakfast? The "vulgar class" (No. 1,321) and the "mischievous portion of the population" (No. 1,320) are abroad at this time, continues the same officer, and 66 66 people of a higher grade would not like to come to the Museum WITH sailors from the dock-yards, who might bring their girls with them” (No. 1,329). And what if they did, so long as they behaved properly! That able legislator, Mr. Ewart, suggested lately, in the House of Commons, that the Museum should be accessible to the public on SUNDAYS, and why not allow this after one o'clock? The luxurious Aristocracy are at liberty to revel in the delights of their Eden, the Zoological Gardens, on a Sunday, and to amuse their fair partners, or girls" if you please, by explaining to them the various habits of living animals, not always the most delicate, particularly those of the monkey tribe bearing so close a resemblance to their monkey-jacket friends of the West-end; they have all this, and more still-they have their numerous. magnificent CLUBS, provided with every indulgence that wealth can purchaseas well as the splendid LIBRARIES of Clubs, where they may lounge and yawn away the whole of their Sunday, or peruse any book they please, from the Bible to Voltaire: but the common people, forsooth, the "vulgar class," the mischievous population," must go to church three times a day, or get drunk at the ale-house; not being rational beings, of course they need no rational recreation!! Their crime is, to be poor, though industrious; they have lost caste, and must be kept down to their situation in life. But these things must be altered;, the people are no longer serfs or slaves, and cannot now be treated as such! They have an undoubted right fairly to enjoy that to the support of which they all contribute their mites, however small they may be. Another accommodation might readily be granted to the publican EVENING READING-ROOM might be built, where thousands would go to consult their own books, for such they are. How many tradesmen and professional men, what numbers of the industrial classes, would hail this as the greatest boon the Government could bestow!! The Principal Librarian says (No. 1,313) the Museum was not intended for lawyers' clerks, at least not for their principal accommodation; and that mer chants' clerks (No. 1,314) would find all they wanted in circulating-libraries. The Rev. Secretary says (No. 1,303), that the Museum is "rather too much than too little used!!" As a further instance of the aristocratic nature of this establishment, it may be stated that the chiefs of departments, when they go before the Board, stand during the whole time (Nos. 2,960, 3,701). Before Committees of the House of Commons a chair is always given to the witness; but we suppose his Grace the Archbishop of Canterbury considers himself to be the King of the Museum! What folly! This should be altered. The subject of an Evening Readingroom was broached by one of the Committee last Session, and its practicability was clearly demonstrated. Indeed, it is now admitted that there is a necessity for an entire reform in every thing relating to the British Museum; and that an enlightened philosopher, Sir HUMPHREY DAVY, for several years a Trustee of that establishment, and perfectly acquainted with its management, was of the same opinion. Writing from Rome in 1829, he says,* what is equally true now:— "There must be a general system of change in every thing belonging to this Institution before there can be any system of radical improvement! It appears to me, that the present moment is the best moment for attempting a radical and fundamental change in every thing belonging to this ancient, misapplied, and I may, almost, say, useless Institution. In every part of the metropolis, people * Davy's Life of Sir Humphrey Davy, vol. ii. pp. 342-344 The whole passage is quite worthy of a place in the Mechanics' Magazine. |