iator, is 1.02777, intermediate between that of the rn and southern hemispheres.' That there is no notable difference in sea-water, That there is no satisfactory evidence that the sea That small inland seas, though communicating perature of the Earth. The superficial temperathe earth, if not entirely due to the heat of the sun, tly influenced by it. Still local circumstances cause erable variations in different places situated under he latitudes. These circumstances will be noticed proper place. logical investigations have proved that the temperathe earth has not always remained the same; but that mates of different countries, and probably the sual heat of the entire globe, have greatly deteriorated, he time when the elephant inhabited Siberia, and stodon, the forests of North America. This subject examined under the articles "Change of Climate," Organic Remains." That h respect to the internal temperature of the Earth, perature of the Sea and of Lakes. The maximum est place, while that which is warmed by the incumbent on this. nd 1820, Mr. De la Beche made numerous exith great care, on the temperature of the Swiss om which he found that between the surface h of 40 fathoms, there was a material variarature. From one to five fathoms, in the month er, the heat was from 64° to 67°; but be- temperature decreased down to 40 fathoms. 90 fathoms, the thermometer stood almost uni°; and from 90 to 164 fathoms, it invariably 5' nter, these experiments were repeated, and it hat the temperature of the water followed the perature of the sea at different depths, accords with the observations already made; the tempenishing to the depth where the fluid attains its sity, below which it remains the same, or at mperature. It appears, however, that there is e difference in the temperature of different seas, epths. Thus Capt. Kotzebue, in latitude about longitude 148° W. when the surface of the early 730, found the temperature 57°, at 25 fa8' at 100 fathoms; and 44° at 300 fathoms. same observer in lat. 30° 39′ S. found a tempe9° 5' at 35 fathoms; and in a similar latitude 196 fathoms. It will be observed, however, ne law is maintained, both in salt and fresh decrease of temperature downwards. But this t variance with the probability of an internal, eat, since the waters arrange themselves in the eir densities, and this would take place, whether of deep seas were cold or warm. ture of the Atmosphere. The atmosphere is of two gaseous substances, called oxygen and nd in the proportion of 20 parts of the first, to ast. From its refractive powers, it has been that the atmosphere reaches to the height of ailes above every part of the earth. at which is constantly radiating from the earth, I by the atmosphere, so that its temperature in mperature of the air is dependent on the heat of the surface, is proved by the well known fact, that it ntly diminishes as we ascend upwards, or recede he earth. Hence, in the hottest climates, there is a a few thousand feet above the earth, to which its ever ascends in such quantity as to prevent perpetugelation. line of perpetual snow, we should suppose would in elevation, (under equal circumstances,) accordthe distance from the equator. It is, however, to considerable variations, probably from local caufollowing table, from Encyc. Britannica, article Clipresents the different elevations at which there is at frost, under different latitudes. ind in such a disposi mould constantly be co play of wisdom and cimates, not only tem erve as perpetual reservoi om the melting of the ice numerable streams, would be uninhabitable. m this table, we learn that there is no regular pondence between the latitude and the height of ual frost, and that the difference in this respect is greater than might have been expected from the ace of local causes. Thus the difference between -ezing height at the equator, and in latitude five deis only one hundred and twelve feet; though at the extreme, from eighty to eighty-five degrees, this nce is upwards of three hundred feet. Much the st difference is in the temperate latitudes, as bethirty-five degrees, and forty degrees, where the eleis from 10,287, down to 9,001, making a difference 86 feet in five degrees. Whether these differences tirely dependent on local causes, we have no means iding. he elevation of mountains to the region of perpetual The earth almost ever ich cannot be traced to are existed since the hist e been elevated, or dee history, nor can these g in arations by uncommon opera and then there happ hich elevates a small Sow causes now ро gh supposed to have It being are apparent, should be fects only of which, are We begin with the " that we may be enabled the instruments of pro ch a disposition of things, as that their sum stantly be covered with snow, there is a strikwisdom and design. Such mountains, in arnot only temper the atmosphere below, but Eual reservoirs of water, during the summer, ng of the ice, and thus become the parents e streams, without which, many regions habitable. CAUSES NOW IN OPERATION ON EARTH'S SURFACE. almost every where presents appearances be traced to causes now existing, or which Ince the historical era. No high mountains vated, or deep valleys formed, within the age can these great effects be attributed to the ow in operation. It is true that occasional uncommon floods of water are made, and there happens a subterranean convulsion, s a small portion of earth, but such effects, ed to have operated constantly, from the rewhich the imagination can suggest, will netisfactorily, for the changes which the surth has undergone since the creation. We nclude, either, that the causes which produaty effects, have entirely ceased, and are unor that they operated with infinitely greater than at present. ute the elevation of mountains, to subterrathe excavation of the great valleys, to floods obvious that these causes must have been infiOwerful at some remote period than at pre e of the great objects of Geology to point out which the crust of the earth has undergone, to account for them; it becomes necessary snow operating, and the effects of which should be distinguished from those, the ef which, are certainly known at the present day. with the "Effects of causes now in operation," be enabled to judge how far they have been to of produc which it the earth has undergone, and how far, with more time, reater force, they might account for the phenomena h the earth presents. eneral effects of running water. It is well known mountains, or lands elevated far above the level of the attract the moisture of the atmosphere, in some proon to their elevation. By this provision, the higher ons of the earth become perpetual reservoirs of wavhich descend and irrigate the plains and valleys below. s a great proportion of the water which falls upon the 1, is carried first to the higher regions; and then made escend, often by steep declivities, towards the sea, so it requires a rapid velocity, and removes a greater tity of soil than it would do, if the rain was equally ibuted on the mountains and plains. Thus without ence to the disintegration or decay of rocks, the waonstantly transports more or less soil and gravel from ills to the plains. mong the most powerful agents in effecting the decay cks, is the mechanical action of water, especially in climates. It is well known that water expands in the -f freezing. The effect of this expansion is so powas to burst bomb-shells, and large cannon, when ely confined in them. When, therefore, water falls the fissures of rocks, and there freezes, the rocks are apart with the force of a powerful lever; and the more us ones are divided into small pieces. These are of Further divided by the frequent fall, and consequent hing and grinding motion of one rock on another on leclivities of the mountains. Water also has the powdissolving considerable quantities of some kinds of s, especially those of the limestone and gypsum kinds. Oxygen of the atmosphere is another cause of the deof rocks. "This element is gradually absorbed by all al and vegetable substances, and by almost all minenasses exposed to the open air. It gradually destroys quilibrium of the elements of rocks, even the hardest regates belonging to our globe."-Sir H. Davy. When earthy matter has been once mixed with running r, a new mechanical power is obtained by the attrition and and pebbles, borne along by the violence of the m. Rapid streams charged with foreign matter, and wn against their rocky sides, will, in the course of time, |