SKETCHES IN GEOLOGY.

West Coast Times, Issue 631, 2 October 1867, Page 4

SK ETCHES IN GEOLOGY.

- - f: Lectuee dehvebkd by M» South, at the Ooitbt House, .oil fhe 12th Sept., 1867, J»f (?# Jty?jcfe for forming a Library in connection with the SoTeitika Literary Society. [CONTINUED.] Most geologists agree in the supposition that the solid crust of the Earth is about ten miles in thickness, and that within a comparatively short distance— say eleyen miles — of our feet, is a sea of liquid firo more than seven thousand miles deep. This is rather a startling proposition, and tends to make one feel rather uncomfortable perhaps; but it is, nevertheless, the conclusion at which tha explorer "of science, gleaned from the great labors of the modern geol.ogists, must arrive at, and to follow out this line of reasoning, we may thus see how little this, which we call the solid portion of our Globe, is really 'worthy of the name, and how thin and fragile ig the fihn enveloping the. fluid portion of the Earth, and how promptly it would, without doubt, be destroyed, "if it were not for the 559 volcanoes distributed over its surface, acting as safety valves, and presenting outlets more or less free to the action of the subterranean fires. The superficial observer generally forms a very erroneous and exaggerated idea of the thickness aud solidity of the Earth's crust, which may (according to M. De Quatrefois) be compared to the thickness of a sheet of thin letter paper for one of those globes generally U3ed in geographical studies, or, as Dr. Lardner has it, "If the egg of a fowl be imagined to represent the Earth, its. shell would be much too thick to represent the solid crust." These statements, however, require to be examined very carefully. They do not mean that this would represent its uniform thickness. Lardner mentions its absolute thickness to. be at Jeast from thirty to forty miles; but this is not so in the truly volcanic districts. In these districts, no doubt lake 3of melted rock exist at probably a smaller depth. According to -Phillips the solid rocks added together would represent a f ew — Ba y ten miles'. experiments in mines, and collieries, 'and deep wells, it is found everywhere that the variable influence of the seasons on the temperature of the Earth becomes insensible at a very small depth (sixty to seventy feet), and that below this depth the heat continually augments by a sensible and nearly uniform rate. In the mines of Cornwall this rate is usually about one degree of Farenheit in forty-five feet of descent, there being some difference between the kind of rock called Jcillas, and the granite. In the collieries of England, the augmentation of heat is less rapid, one degree for sixty feet being a general mean. In Ar,ter sian wells very similar results obtain." -The depth assumed by M. Bischoff in his. "Theory of Volcanoes" is, that at a depth of eigbi or twelve miles the temperature is probably about 1000 degrees, high enough to melt spme of the more fusible rocks ; and at twenty miles or thirty, 2000 or 3000 degrees, a heat at which few substances could remain solid.? unless an obstacle to fusion be caused by the augmented pressure experienced at such depths. The precission of the equinoxes (a phenomenon depending on the attractions of the sun and moon on the spheroidal surface of our rotating planet) has been made the Subject of a celebrated memoir by Mr Hopkins, in the Phil. Trans, for 1839-40 and 42, for the purpose of discovering the depth of the solid crust of the Earth. He assumes, with the consent of all the astronomers and mathematicians who have considered the subject, Ist. — The former fluidity of the Earth. 2nd. — Its actual rotation, and the attraction amongst its particles. 3rd. — The density increasing with the pressure towards the centre on every radius, or semi-diameter of a circle ; that the interior surfaces, of equal pressure and equal density are also concentric (i.e.. having one common centre) and spheroidal, or oblong, and have their axes in the axis (or revolving line) of rotation. The result being, taken in connection with nutation (or a land of tremulous motion) of the Earth's axis that it was found, the thickness is not less than one-fourth or one-fifth of the radius of its external surface. Connected with these recent legibly scientific investigations, and combining such, these facts with the general conclusion of Mr Hopkins, we see clearly that solidification has proceeded downward from the surface far enough to reduce to large masses all the fluid matter near to the surface, or capable of being raised to it, and this attended with vast irregularities in the thickness of the crust. Phillips arrives at the conclusion that the Earth in some parts appears to be solid, or to contain solid parts principally for 800 or 1000 miles in depth from the surface. That it is not universally solid the floods of melted rock which occasionally rush out of volcanoes suffisiently prove. A later analyst, Mr Hennessy, assigns a less dej,th, but still one greatly exceeding the conjecture of Bischoff and many geologists. But we must not expect to ascertain more than is possible. We, here in New Zealand, call the inhabitants of England our antipodes, because they walk with their feet exactly opposite to ours. When we stand perpendicularly upright, they hang perpendicularly downright. If the Earth were transparent, we should have a full view of the soles of their feet, with the rest of their persons foreshortened, as the painters call it. The men in the moon, on the contrary, are exactly our anticephahv. Ido not mean to say there are any. It is merely put here for sake of my argument. Their heads are opposite to ours, and if the intervening space were annihilated, we and they should, as it were, be laying our heads together! Consequently, could any telescope show us an inhabitant of the moon we should see him exactly, as we look down on a passenger in the street, walking upon the pavement beneath a third storey window. We could only see the crown of his hat, his shoulders, the point of his nose, the tips of his toes, and perhaps the equatorial regions of his corpulency. To know what he is really like, we should have to request him to lie down on the flat of his back, and then to roll over and show his other side ! We do gain, though, one advantage by our relative position with that of the Moon, we can peep, and have peeped, down the immense craters of the Moon's volcanoes by the aid of Lord Eosse's gigantic telescope, and see what there is inside them, and no earthly volcanoes can give any idea of the chaotic desolation reigning there. But whilst it would be unwise to conclude that we know accurately the rate at which the heat of the Earth increases downwards, the progress of science certainly appeal's to confirm the doctrine of central heat. The action of heat in the formation of primitive rocks cannot consistently be doubted in connection with theßO investigations, based as they are on theories and hypotheses reduced to practical demonstration by the great mental culture and subsequent labor of geologists ; but this is in reference to scientific calculations connected with the materials within our Globe. To those who are not acquainted with it, however, the astounding filet remains to be told, (and which goes strongly to prove the action of heat in the formation of primitive rocks) thin nearly every mineral and metal in the criiifc of the Earth has been produced artificially by imitating the processes of nature. <£ gf fbgtffa )p* pmves tip

series of experiments, begun by Mitscherlich, to work this out. Ebehnan astonished the last generation of reading people by making jewels. He found that boracic acid entered into the composition of several minerals, and forms 31 per cent, of alumina and 39 of silica. This acid Ebelman used as a solvent at a high temperature, and then evaporating the solvent, produced among other minerals, rubies, sapphires, chrysolite, and chromate of iron. Ho pounded emeralds, and then fusing the dust with boracic acid, and a little oxide of chromium, reproduced, or rather made, new emeralds. Metals can be produced artificially like minerals, and even gold can be made, but (something remains to be mentioned in connection with this) at double the price of the natural production. M. DauLree has recently extended considerably the list of artificial minerals and metals. With other minerals he has obtained quartz and felspar, clay having been previously purified by washing, under this process, produced felspar and crystals of quartz. Buffon tested his ideas of terrestrial heat by setting up great furnaces near Montbard, into which he put balls or bullets of iron, copper, and minerals, as like as possible to those composing the crusfc of the Globe. These large balls he heated up to the degree in which he supposed the Earth was at first, and then watched the time they took in cooling. Applying the ratios arrived at in these ways, he reckoned that from the incandescence of the Earth to his time, a period of 75,000 years had elapsed. Life, he calculated, had existed upon the Globe 35,000 years, and the future duration of life upon it could not, he concluded, exceed 93,000 years, when, he said, vegetation would die of cold. Fourier, the author of the " Mathematical Theory of Heat," took Buffon up on his own ground, and, by refuting him, drove away his xmcomfortable hypothesis. He accepted, as proved, the notion of a general sea of fire ; and did not deny the alleged thinness of the crust. Buffon, according to Fourier, erred when he supposed that the cooling was still going on at the rate at which it began. So the Earth will not, some 90,000 years hence, die of old age. "Of course," says a pleasant writer on this, " of course we are all glad to hear it, even for the sake of our descendants, a million generations after us !" All of the present land has been under the sea. In Mr Robert Chambers' interesting work called the "Ancient Sea Margins," will be found an accumulation of facts and observations on the subject of sea levels. The island of Great Britain, he says, was once submerged at least 1700 feet. "What, indeed, if we consider, does the dry land chiefly consist of but ancient sea beds, and the matter of igneous irruptions. No doubt now exists amongst geologists that New Zealand is but a pait of a great continent which has been submerged. Sir Chai'les Lyell remarks that it is known that in the earthquake in the Northern Island of New Zealand, in January, 1855, there was a permanent rise of land on the northern shores of Cook's Straits to the extent of nine feet vertically. On one side, Mukomuka Point, or immediately to the east, there was no movement, while on the other side, or to the westward, there was a gradual diminution of the uphpaval from nine feet to a few inches, until, at a distance of twenty-three miles, no change of level was perceptible. Simultaneously with this elevation of land there was a sinking of the low coast to the amount of five feefc in the Middle Island, South of Cook's Straits. No doubt the repetition of »uch unequal movaments may, in a time, geologically brief, turn parts of any valley into a lake. No one who has examined the works of modern geologists can reasonably arrive at any other conclusion than that the present continents of the Globe, with perhaps the exception of some of the very highest mountains, have, for a long period, constituted the bottom of the ocean, and have been either subsequently elevated into their present position, or the waters havo been drained off from their surface. This is probably the most important principle in Geology, and though often regarded with doubt, it is as satisfactorily proved as any other principle of physical science, not resting on absolute mathematical demonstration. Nothing, perhaps, has puzzled men of science more than the fact that at what are now the Poles of the Earth, and where there is almost perpetual frost and snow there once abounded a rich tropical vegetation, equal and similar to that of Lidia and Africa at the present day. We are certain of this, not only from the presence of trees and shrubs which have been preserved in a fossil state, but more particularly by the presence of the remains of animals who could only have lived in a very warm climate. There are the bodies of the hippopotamus and rhinocerous, as well as the mastodon, found imbedded in the ice, almost as perfect as when they died; and on the shores of the Frozen Ocean there are countless skeletons of the mastodon who all lived and died, and were buried in or near the spot where they are now found. How was it, then, that such animals could exist near the Pole, when, at the present time, no animal of the kind could live within thousands of miles of it ? The true explanation is that the Earth has another motion of its own, and that so slow as to be beyond calculation just now, but it is no less certain. Most of the eminent geologists and geographists of the day have arrived at the result, that; the Earth is nofc only subject to the changes of being transformed from dry land to the bottom of the sea, but the Poles have been the tropics, and the same tiling will assuredly happen to every other zone. When, however (we may ask), were such mighty changes effected? Two thousand years and more have elapsed since the Earth's surface and size hare materially or perceptibly .changed. Vast, but very gradual changes in the continental masses have undoubtedly wholly changed the climate of particular regions, and in this is involved one grand question, namely : Do such changes proceed from irregular and accidental force ? or is it in obedience to tho mandates of a power without, and above the mere physical agents which are employed to do the will of the Great Architect of the universe for its ultimate preservation, and that by some great compensating laws with which we are wholly unacquainted? Wo do know that whatever changes may take place in the materials of ■vrliich this Earth is formed, that the most infinitesimal e atom is preserved, and that into whatever they are resolved, they are assuredly indestructible. I have been referring to irregular and mighty changes and their probable causo, and no greater instance of such have occured anywhere than iv t'uc islands of New Zealand. The rocks composing the Pelorus ranges and the Wellington ranges are of identical geological formation, but by some great force (most probably that of igneous action), have been severed. There arc evidences of the Northern Island, at that period, having remained stationary, whilst some gigantic force (remarks Dr. Hockstet(er) has pressed the great mass of the Middle Island to the westward. The most recent accounts showthat the sea is constantly making aggressions on the present coastline of parts of the Middle Island — that sea which ages ago washed the bases of our mountain ranges, forming the vast debris which remains comparatively unexplored. Notwithstanding tho large amount of gold extracted from the alluvial terraces, the gravel accumulation, the river terraces, and beaches, the true bottom has, except in few instances, scarcely been tested. All who have given the subject attention concur with me that the goldfields of the West Coast arc but in thoir infancy, and years honce (although some of us may not live to see it) associated enterprise will be followed by startling results, ending in a bright future, (To be fipritinucfi.)