is the lessons embraced by the preceding chapters and sect. ons, I have endeavoured to explain to you the parts, which tire nd running water have acted, in effecting changes on the crust of the earth. Our new chapter brings us to another class of powerful agents, which exert an unwearied agency in changing the surface of the globe. We have now to examine the decomposition, disintegration, and decay produced in the earth's crust by meteoric agents or atmospheric influences. By these atmospheric agents and influences, I mean the gases of the air, heat and cold, dryness and moisture, rains and winds, light and electricity. The operations of these slow but incessant agents, assisted by the laws of gravity, form a vnde-spread system of disintegration and destruction which aay be traced over the whole surface of the earth, from the pinnacles of the highest mountains down to the level of the sea. There is no rock, however hard, that does not bear some marks of what is termed weathering, or some traces of the action of the atmosphere upon it. All the mineral substances of which any rock is composed are well known to have greater or less tendency to combine with the oxygen of the atmosphere, especially when under the favourable circumstances of changes of heat and moisture, and probably of light and electricity. Carbonic acid and water, also, are perpetually absorbed by rocks in considerable quantities. The change which the atmosphere produces in the surface of rocks is exceedingly variable, and depends much upon local circumstances. A rock of the same mineral composition which may undergo complete decay in one situation, will in another suffer but a trifling disintegration. The result of these combinations between meteoric agents and rocks, whether the action be chemical or mechanical, is to loosen the coherence between the particles on the surface, and to induce a tendency to decomposition and destruction, or what is commonly called, crumbling. It is impossible to contemplate the surface of mountains and valleys, of continents and islands, without being struck with the stupendous effects of the slow but constant and long progression of atmospheric agency. These effects, by the slowness of their operation, and comparative diminutiveness of their day's work, attest a lapse of time and ages far beyond all calculation. The operations of atmospheric agents upon rocks are, perhaps, best studied in granite countries, or in districts of red sandstone and shales. The Tors and the Logan stones of Devon and Cornwall may be mentioned as excellent specimens of the weathering of rocks. These specimens become the more striking by the circumstance, that granite is so little subject to change as to be proverbially used as a symbol of endurance and immutability, and is on that account selected as the material for the erection of bridges and great national works of architecture. Nevertheless, granite, under particular circumstances of texture, climate, and exposure, is remarkably liable to disintegration. The Tors of Dartmoor and the Logan stones of Cornwall are composed of granite, which, as you may see in the blocks of Waterloo Bridge, are divided into masses of cubical or prismatic shape. Through the influence of the atmosphere or weather, the particles in the hard surface of the granite, which are most exposed to the air and rain, become loosened and separated, and the masses, which were originally prismatic, acquire an irregular shape. In short, the rock crumbles into shapeless gravel. The amount of the disintegration, and the immense lapse of time which the atmospheric operation occupied, is indicated by the depth of the crumbled surface of all the districts around these Tors and Logans. Indeed, in any area, whatever may be the nature or the mineral character of the rock, whether porphyry, slate, compact sandstone, or trap, the surface is found shattered, and crumbled to a considerable depth. The phenomena of this weathering and crumbling throws light upon other operations which have taken place in the early history of these disintegrated rocks. They evidently prove that the valleys of the neighbourhood had been formed, by other agents, long before the process of decomposition by weathering commenced on the surface; for they shew that the general outline and form of the land, in hill and valley, In the above diagram, the curved line A B C shows the disintegration of the granite rock &o, following a line of previous elevation and depression. A part of the rock, from a to y, on account of some peculiarity of lithological composition, has been able to resist the influence of the atmosphere so as to show very little weathering. The influence of moisture and frost is seen to have entered the body of the rock somewhat deeply, and to have crumbled much of its mass under the surface soil. In the valleys below A and c, the accumulation of the detritus is greater than on other parts of the line. This was to be expected. It is obvious that the weather-worn particles, disintegrated on inclined planes, will very often fall by their own gravity from their original position, and their downward progress towards the valley will be increased by the action of showers of rain or that of melted snow. As this process goes on for years and ages, the quantity of detritus accumulates in some instances to a very great depth. When this accumulation of weathered materials has been cut through by a rivulet, or in making a new road, it sometimes has a stratified appearance, as if the loosened and crumbled fragments from the hill sides had slidden or slipped over each other at the bottom of the valley, as is faintly represented under a and b. Such is the extent of this disintegration in granite, that it is found in the quarries at Dartmoor to the depth of fifty or sixty feet, as represented by the cracks in the diagram. Fig. 70. A Logan Rock, Cornwall. In Cornwall, and other places, this action of the weather has, in several instances, worn away part of the jointings of large blocks of granite, which are, consequently, left resting on a kind of central pivot. From this circumstance, these masses of weathered granite can, notwithstanding their enormous bulk and weight, be easily moved. Stones in this position are Another invisible and mighty agent of destruction contained in the atmosphere is oxygen gas, which acts powerfully upon different rocks according to the elements of their composition. This gas is peculiarly destructive to rocks which have iron in On the surfaces of some granite rocks are frequently found their composition. Whenever you see reddish brown stains on strangely-fashioned holes, which are called Rock-basins, which the surface of weathered rocks, you may be sure that such some antiquarians have ascribed to the hands of the ancient rocks contain some compound of iron. The reddish stains are Druids, but which, in fact, are due to the silent and slow occasioned by the efforts of the moisture of the atmosphere to chisellings of the invisible gases of the atmosphere. These holes decompose the iron and to cause it to be dislodged and reconsist of several basins, apparently hewn out of the rock, some moved. The oxygen unites with the iron, and by this combiof which are eighteen feet in circumference and six in depth. nation loosens the particles of the rock. The result of this At Peninnis Point, in the Scilly Islands, there are curious operation is, that the hard rock becomes cracked, crumbled, and examples of these basins. In that locality they are called by softened, until, at last, it becomes pulverized dust. As this the peasants, "the Kettle and Pans." They occur in the sur- gas is soluble in water, though it be but slightly, it may, in its face of immense blocks of granite on the top of the promon-dissolved state in rain water, exert a destructive power over tory, and are about three feet in diameter and two in depth. the surface of rocks which are pelted or moistened by the Most of them are nearly circular, but many of them have swerv-winter shower. ing curves on the edges, some of them have their sides perfectly perpendicular and their bottoms flat. The granite blocks in which these rock-basins are found are six or seven yards high, with surfaces of eight or nine yards square. In some This atmospheric agency in weathering and disintegrating the surface rocks of the earth's crust has produced great bene fits to the world. The effects of the combined operations of all these atmos pheric and gaseous agencies are finely illustrated in the holes, caverns, arches, and avenues, sometimes of most grotesque shapes, which are found in rocks of all descriptions. One of the rocks in Capri, an island near the coast of Naples, furnishes a good illustration. The rock consists of lava, weathered into crevices and passages of the most fantastie forms. It is to this silent but powerful agency that we are indebted for all our porcelain clays. Your earthenware jug and flowerpot, and your splendid and costly china dishes and vases, are produced from a material which is formed by the combined influences of moisture, air, and carbonic acid. The rocks from which these different clays were derived may have been of various mineral character, but they all agreed more or less in the chief ingredients of their composition. About Dartmoor and in Cornwall there are rocks of a fine white granite, which present striking examples of the disintegration effected by the weather. On their surface, and to a considerable depth in their substance, the rock is altered to a soft matter resembling mortar. This soft matter is disintegrated granite, and is collected together and washed. The water that washes it is conducted into tanks, where it deposits a white earthy matter which constitutes the beautifully white fine clay employed in the manufacture of porcelain. Not less than ten thousand tons of this white clay, the produce of the weather upon granite, is exported every year from Cornwall for the use of the English potteries. The facts are the same as to the clays employed by the Chinese in their exquisite porcelain. What I have said of porcelain clay is, in a measure, true of all other clays. Porcelain clay is white, but earthenware clay is more or less yellowish, brown, and even red. This difference in the colour does not essentially depend upon any difference in the formation of the clay as clay, for each clay is derived from the decomposition of feldspar. The reason of the difference is this. Some rocks which contain feldspar contain also iron, or some colouring matter which communicates its stain to the clay derived from it. The signal fact, however, which makes this atmospheric action upon rocks more important than any other instances of it, is the disintegration of the surface of rocks which contain silver and gold, a fact that has charmed thousands to California and Australia. Many have wondered how silver ore came to be discovered in such out-of-the-way situations as the bleak and craggy summits of the Andes of South America. Atmospheric agents will answer all the questions upon these topics. Granite, porphyry, and slate are hard rocks, but silver ore is harder still. While the rocks which contain veins of silver are readily decomposed and crumbled away by air and weather, the sturdy metal will resist these influences. The consequence is, that, as the surface rock weathers and moulders away in the cliff, the veins of silver will come at last to project and stick out from the side of the rock, and these jutting masses will be seen and marked by the first visitor. One of these valuable mines was discovered by a driver, who had to throw a stone at one of his loaded donkeys while passing over the Cordilleras. Finding that it was heavy in the throw, he picked it up when he came to its place, and found that it was full of pure silver. cially in the district called Delta, the atmosphere is filled with exhalations from the neighbouring Mediterranean Sea. Here the ancient cities, Memphis, and Heliopolis, built of massive granite, are now mere heaps of ruins. Not only do not the stones lay one on another, but the very blocks are crum bled by the weather. Even the proud granite obelisks at Alexandria are becoming more and more unreadable through the corroding action of the weather upon the inscriptions. If you leave the Delta, and travel on to Upper Egypt, you find that there, in an atmosphere not favourable to disintegration, the monuments, the tombs, and the inscriptions, exhibit no signs of decay, but appear as well defined and as fresh as if they had just come from the artist's chisel. Even the black bricks, made of the mud of the Nile and dried in the sun, and exposed to the atmosphere for three or four thousand years, still retain their hardness, and firm position in the temples, pyramids and tombs, and present their hieroglyphics and architectural ornaments as distinct in outline as in the first year. LESSONS IN ENGLISH.-No. XLIX. in the singular and in the plural haddock, pike, ray, salmon, These deviations from analogy, though strictly proper, inasmuch as they are justified by authority, are not to be extended analogically, and there seems to be a disposition to bring some of them into conformity with rule. Thus we say, "the chamber is twenty feet long and ten feet high;" also, "I have paid you four pounds;" whereas the phrase used to be four pound. Some words in their nature do not take and others do not admit of a plural form. Collective nouns, such as fleet, sail, &c., having in the singular a plural import, do not take a plural form. Abstract nouns, such as whiteness, knowledge, progress, being in their nature restricted to unity of idea, do not admit of a plural form. Sometimes, however, the idea which an abstract noun conveys, is considered as distributed, and then it may assume a plural form, as truths, virtues, sanctities. This use is to be strictly limited by a regard to authority. A latitude here gives either an affected or poetic air to composition, e. g., as when a young writer speaks of mer," "the chills of autumn," or "the sanctities of the hearth." The following words are used exclusively in the plural, namely, such as, consisting of two parts, have before them the term a pair; as A pair of bellows. The diggings of gold, delved in the sands of rivers and valleys in California and Australia, furnish other examples of the disintegrating influences of the weather. Gold is scattered in small particles through the substance of various ancient rocks. By the incessant. wearing down of the surface of these rocks," the frosts of winter," "the rains of spring," "the heats of sumthese gold particles are set loose, and then, either fall from the sides of the rock, or are washed away and transported by rains and mountain torrents, to valleys at a distance from their native rock. In this lesson I have spoken of atmospheric action upon rocks as being much modified by favourable circumstances, which means circumstances of climate favourable to disintegration. This fact can be verified in any country or district, for all parts supply illustrations of granite, porphyry, limestone, &c., disintegrating rapidly in one place, while their decomposition is almost imperceptible in another. In no country, perhaps, can we find examples of this so palpable and so decisive as in Egypt. The operation of these causes of decay, rapid where the atmosphere is charged with moisture, or where rains and winds are prevalent, but imperceptible where moisture is absent, is clearly illustrated in Egypt. In Lower Egypt, espe breeches. colours. A pair of nippers. " A pair of snuffers. spectacles. ,, tongs. trousers. tweezers. When the words a pair is the subject of the proposition, the verb must be in the singular; but when a pair is dropped, and a word such as bellows, drawers, &c., is the subject, the verb must be in the plural, e. g. This pair of breeches is too small. Metaphysics, the science of mind. Boardwages, wages for mere sub- Nuptials, ceremony of marriage. sistence. Bowels, the entrails. Calends, the beginning of the month with the Romans. Clothes, vestments. holds. Customs, taxes levied as import duties. Downs, hillocks of sand on the sea coast. Draughts, a game of skill. Effects, a man's personal property. Ethics, the science of morality. Greens, cabbage, &c. Oats, a kind of corn. Pneumatics, the science of at- Politics, the science of government, Quarterings, the coats of arms in Quarters, station for soldiers. Shackles, chains, impediments Statistics, the science of facts foun- Subsidies, supplies of men and you. Tactics, modes of proceeding. Intestines, the bowels. Lees, the sediment in wine. Names of persons may be in the plural when more persons than one are intended, as, the two Catos, the Scipios; also when a proper name is used descriptively, e. g., the Ciceros of the age are few; the Ciceros, that is, the great orators. Hence good English usages would require the Miss Smiths, the Mr. Dobsons. Regard to French idiom has, however, for some time required the firm of Messieurs Potter and Norris, or Messrs. John Wilson and Sons. There is, therefore, some excuse for the affectation now almost constantly seen, when two sisters open a ladies' school, namely, the Misses Brown or the Misses Tinker. Such deviations from pure English require to be checked. EXERCISES.-COMPLETE. Vitals, the parts of the body on Had we space, we might be able to assign the reason why these nouns severally are used in the plural only. One instance may be taken. There is a class of nouns, such as acoustics, physics, metaphysics, &c., which claims attention. These words are of Greek origin. They in each case denote a science, and they are in the plural because our English translators put into the plural the several corresponding Greek words, which are in the plural, when first they rendered the Greek terms into English. Thus, in translating Aristotle they found the science of material things, called ta physica, that is, Aristotle's treatise on material things, and so, in servile obedience to their Greek master's usage, they coined the word physics. Another treatise by the same authority was designated meta ta physica (things to be studied after physics,) which consequently they rendered metaphysics; that is, the science of mind, to which Aristotle thought the student should apply not till he had mastered the science of matter. EXERCISES.-INCOMPLETE. The tree is full of. She is a lovely-. That child has the hooping-cough, it must not play with the other. Yesterday I saw one black mouse and two white. Our cook has bought a fat goose; are-cheap in this place? Have you a penny? Yes, here are six-which make six-. In London there are more than six hundred (church). In the United States of America the-are |