some even reach the temperature of boiling water. The hot springs of La Trinchera, situated three leagues from Valencia, form a rivulet which, in seasons of the greatest drought, is 2 feet deep, and 18 feet wide. Their temperature is 90.3 centigrade, or 195° of Fahrenheit; but that of the springs of Urijino, in Japan, is 212° of Fahrenheit. Eggs placed in the Trinchera springs are boiled in four minutes. At the distance of 40 feet from them, are other springs entirely cold. Rocks are frequently formed by depositions from the waters of hot springs. The well-known hot springs of San Philippo, in Tuscany, have formed a hill of calcareous tufa, in many places as compact and hard as limestone. The ancient temples, and the gorgeous palaces and churches of Rome, and indeed the whole of the streets and squares of the former Mistress of the world, are built of concretionary masses, which, according to Professor Jamieson, have been deposited by springs. Many cold, or common perennial springs, throw out great quantities of calcareous matter, of which we have an example at Starlyburn in Fifeshire.

Various have been the opinions of philosophers concerning the origin of springs; but those which deserve most notice are the three following : 1st, That the sea-water is conveyed through subterraneous ducts, or canals, to the places where the springs flow out of the earth; but as it is impossible that the water should be thus conveyed to the tops of mountains, since it cannot rise higher than the surface, some have had recourse to subterraneous heats, by which being rarefied, it is supposed to ascend in vapours through the bowels of the mountains. 2d, Others, advance the capillary hypothesis, or suppose the water to rise from the depths of the sea, through porous parts of the earth; but they seem to lose sight of one principal property of this sort of attraction, for though the water rise to the top of the tube or sand, it will rise no higher, because it is only by the attraction of the parts above that the fluid rises. Therefore, though the waters of the sea may be drawn into the substance of the earth by attraction, yet it can never be raised by this means into a cistern, or cavity, so as to become the source of springs. The 3d hypothesis is that of the sagacious naturalist, Dr. Halley, who supposes the true sources of springs to be melted snow, rain-water, dew, and vapours condensed. The Doctor found that every ten square inches of the surface of the ocean yield a cubic inch of water in vapour per day, every square mile 6,914 tons, and every square degree, or 69 English miles, 33 millions of tons. Now, if we suppose the Mediterranean to be 40 degrees long, and 4 broad, its surface will be 160 square degrees, from whence there will evaporate 5,280 millions of tons per day in the summer-time. The Mediterranean receives water from nine great rivers, viz. the Ebro, the Rhone, the Po, the Danube, the Dniester, the Dnieper, the Don, and the Nile; all the rest being small and their water inconsiderable. Let us suppose that each of these rivers convey ten times as much water to the sea as the Thames-which yields daily 76,032,000 cubic feet= 203 millions of tons; all the nine rivers will produce 1,827 millions of tons; which is little more than one-third of the quantity evaporated each day from the sea. The prodigious quantity of water remaining, the Doctor allows to rains, which fall again into the seas, and for the uses of vegetation. As to the manner in which these waters are collected, so as to form reservoirs for the different kinds of springs, it seems to be thus: The tops of mountains in general abound with cavities, and subterraneous caverns formed by nature to serve as reservoirs; and their

pointed summits rising into the clouds, attract the vapours of the atmosphere, which are in consequence precipitated in water, and by their gravity easily penetrate through beds of sand and lighter earth, till they are stopped in their descent by more dense strata, as beds of clay, stone, &c, where they form a basin or cavern, and working a passage horizontally, issue out at the sides of the mountains.

Rivers.] The effusion of springs, and the flowings of melted ice, form little currents more or less gentle, which are termed rivulets. The union of two or more of these currents forms streams, which, following the declivity of the ground, unite most frequently before they reach the ocean in one large stream or river, which conveys their collected waters to the sea. It is evident, that if the earth were a perfectly level surface, no river could exist; for when water flows in a current or stream, it does so in consequence of the end of the channel towards which it is floating being lower than that from which it proceeds. But the rapidity of a river does not always depend upon the degree of its declivity. Thus the Danube is much more rapid than the Rhine, although the bed of the latter is much more inclined. This is owing to the greater volume of water, The Inn, which forms the main southern branch of the Danube, is a far more rapid stream than its rival, and rushes quite across the Danube at Passau. The reason is obvious. For, supposing the volumes of both to be equal, or nearly so, the Inn has a slope of 6000 feet to traverse, and the other only 1200 feet of slope to traverse previous to their union at Passau, the superior degree of declivity being as 5 to 1. The Danube is a very broad stream after passing through Hungary, being fully two miles broad at Giurgevo, and interspersed with islets, and having very low banks, and cannot therefore be very rapid. It is where the channel is deep and narrow in proportion to its volume of water that a river is most rapid. Three things must concur to make a rapid riverthe impetus with which the stream is propelled at the source; the great continuity of slope; and the quantity of water successively poured in on both sides, from slopes equally great. The most rapid known streams are the Inn and Rhone, in Europe; the Platt and Missouri, in North America; and the Whangho, in China. The comparative velocity of the great rivers of the globe is not yet known, otherwise than by inference from casual observation, volume of water, and degree of slope. When the fall of a river is sudden, and its course extremely quick, it forms what is called a rapid; and when it throws itself suddenly over a rock, it is called a fall or cataract.

The strength of a river depends upon the volume of water which it contains, and the rapidity with which it flows. In general, the streaming of a river is strongest in the middle of the current; the elevation of the water is also greater there than at the sides. But the water stands lowest in the middle at the mouth of rivers, because the water of the sea mixes with the sides of the fresh water current. Some rivers, like the Danube, rash with such force into the sea, that their waters are distinguishable for a considerable space from those of the ocean. It is only by a very large mouth, like that of the Elbe or the Plata, that rivers can quietly discharge their waters into the ocean. The river of the Amazons exhibits a terrific spectacle twice a-day at its mouth, when the two tides of fresh and salt water meet each other. The quantity of water which some rivers discharge into the ocean is enormous. But until we know with precision the mean annual average of rain for every parallel of latitude,

or have obtained accurate soundings of the rivers, and by a train of annual experiments on each, determined their rate of increase and decrease, and of accelerated and diminished velocity, it is not possible to obtain any positive results on this subject.

The change which the action of rivers is constantly operating upon the districts through which they pass is considerable. Many of them now flowing through large vallies, seem to have excavated these vallies by the silent action of their waters through an unknown course of centuries. Some of them, such as the Elbe near Pirna, and the Hudson in America, have actually worn a channel for themselves in the solid rock; but never could a river by its own force alone have opened for itself a passage through solid rocks similar to those which border the Upper Rhine; it must at the first have found the outline of its course deeply marked out. Some rivers sink into the earth, and run for a considerable distance under ground. Great inundations of rivers are occasionally produced by the sudden melting of snow and ice. In the hotter zones, where heavy rains fall periodically, all rivers are subject to annual inundations.

Lakes.] Those collections of waters surrounded on all sides by the land, and having no visible connexion with the sea, nor any perceptible current, are called lakes. There are a vast number of lakes scattered over the surface of the earth; but the largest belong to North America. They may be divided into four classes.

The first class comprehends those which are not supplied by any river or brook, but give origin to streams. These are doubtless fed by springs, which well up in the bed of the lake till they reach a level, where they find an outlet. The largest rivers originate in lakes of this class, which, as they receive no stream, must necessarily in most cases be in elevated situations.

Another class of lakes is very numerous, consisting of all such as receive and discharge streams of water. When a river encounters a large hollow in its course towards the ocean, it must necessarily fill this basin to its own level, and thus form a lake, before it can pursue its course. These lakes have often springs of their own also. Sometimes several rivers empty their waters into a lake, which discharges only a single stream at the lowest point of the shore. In such cases, the river which proceeds from the lake usually receives the name of the largest of the streams which run into it. The largest lakes of this class are in North America.

The above two classes of lakes are the most common. The phenomena of the other two classes are of more difficult explanation. The most remarkable lake of the third class is the Caspian Sea, which receives the tributary waters of the Volga, amounting by the best calculations to 518,400,000 of cubic feet per hour, besides several other streams: and that without any perceptible increase of bulk, though it has no visible outlet by which it can discharge its superfluous waters. Besides the Caspian, and its neighbour the Aral lake, there are several other lakes of this class in the steppes of Asia, and the deserts of America; and the great question which they suggest is What becomes of the waters which they are constantly receiving from their tributary rivers, and from the precipitation of the atmosphere? Some have asserted that this lake, and others exhibiting similar phenomena, stand in connexion with the sea by means of subterranean canals. But this is cutting the Gordian knot, instead of loosing it, as no evidence has yet been produced demonstrative

of the existence of such canals. Tooke has suggested, that the true reason of the Caspian Sea remaining equally full, may perhaps be found in the quality of its bottom, which consists, not of a thick slime, but of a shellsand, the particles whereof touch but in few points, and consequently form a porous bottom, through which the water may be filtered, and fall into the abyss beneath. This solution of the difficulty is not satisfactory; but it may be observed, that the mountains to the south of the Caspian are very spongy, and abound with springs, which proves either absorption, or a very strong evaporation. Perhaps the latter principle is sufficient to account for the phenomenon. In the valley of the Missouri, a climate as cold as that of the Caspian, the evaporation is so great, that a table-spoonful of water placed on deck was evaporated in a very short space of time, and the ink-case had to be daily replenished with the fluid during a voyage of 1000 miles downwards from Fort Mandan, in 47° N. Lat. The evaporation on the river was so great, that though more than 20 rivers of large volume fell into the Missouri in that space, it was not sensibly enlarged. Now, the case is just the same with the Caspian Sea. There is a continual travelling, so to speak, of fluid from the sea to the mountains of Caucasus and Elboors, by way of the atmosphere, and from these heights again to the sea, by the rivers and torrents which water its slopes and traverse its sides. The Aral Lake is not equal to 1-10th of the Caspian in square surface, although it receives two great rivers, the Oxus and the Jaxartes, whose waters, if united, would equal those of the Volga, and yet it is never increased. The same answer must be returned as in the case of the Caspian, that as much goes off by evaporation as is received from these rivers. The case is exactly the same with all lakes which receive rivers but send out none, as those of Maraugha and Van, in Koordistaun, of the Dead Sea in the Holy Land, and the Lake of Zarang in Sigistaun. It seems to be an established fact, that the terrestrial surface is getting drier gradually, though imperceptibly, perhaps. The Lakes of Maraugha, Zarang, and the Dead Sea, are sensibly diminishing, and the volume of the Volga is decreasing sensibly. The Lakes of Canada are said to increase and decrease for alternate periods of so many years.

The fourth class comprehends those lakes which neither receive nor throw off any visible stream of water. These lakes are in little distinguishable from ordinary ponds, which enlarge or contract their dimensions according to the state of the atmosphere. In this class we may

include those collections of water called fens and marshes. These are often covered with a thin vegetation, which either rises from the muddy bottom of the lake, or forms a kind of floating net-work upon the surface. The depth of lakes is very various. Near Boleslaw in Bohemia, there is a lake of unfathomable depth, which sometimes in winter emits blasts of wind sufficiently strong to raise up in the air pieces of ice several quintals in weight. Some lakes vary in depth from one foot to one hundred fathoms. Lake Erie in North America is said to have been rising gradually for the last six years. The water of some lakes is very pure and transparent; that of others turbid. Some are salt and brackish ; others sweet and fresh. Middle Asia possesses a great number of salt lakes, which acquire their saline particles from the surrounding soil.3 Some

"There are several lakes on the face of the earth which have no outlet towards the sea, all the water which falls into them being again removed by evaporation alone, and such lakes are never of fresh water, because every substance, which, from

inland lakes, such as Loch Lomond, are remarkable on account of their frequent violent agitations from unknown causes. Some lakes never freeze; others in high latitudes, or those covered with the shade of thick forests or high mountains, such as Loch Winnoch, remain covered with perpetual ice. Saussure estimated the mean temperature of the Swiss lakes at 42°. Such lakes as contain a large proportion of naphtha and sulphur, and such as have no visible outlet, give out noxious exhalations, which are highly prejudicial to organic beings, and the influence of which is felt at a considerable distance from their shores.

Some lakes exhibit the same phenomena as the intermittent springs, and doubtless from the same causes on a larger scale. There can be little doubt that deep lakes have frequently been converted by the action of streams into extensive valleys. Thus the Spey is met by a barrier of red sandstone at Fochabers, which must have converted a very extensive tract of country behind into a lake. At the village of Rothes, it is met by a much higher barrier, which must have occasioned a re-stagnation all the way to Kenrara; and the hollows seen on the rising grounds to the west of this village, show that the river had formerly flowed over the top of this barrier, and had frequently altered its course before settling in the present channel.

Earthquakes.] Earthquakes, says Dr. Shaw, are unquestionably the most dreadful of the phenomena of Nature; and are not confined to those countries which, from the influence of climate, their vicinity to volcanic mountains, or any other similar cause, have been considered as more particularly subject to them. Their effects have often been felt in the British Isles, although not in so extensive and calamitous a degree. The most remarkable earthquakes of ancient times are described by Pliny in his Natural History. Among the most extensive and destructive of these, was one by which thirteen cities in Asia Minor were swallowed up in one night. Another which succeeded, shook the greater part of Italy. But the most extraordinary one described by him, happened the beginning of time, rain could dissolve in the regions around them, has necessarily been carried towards them by their feeding streams, and there has remained. The great majority of lakes, however, being basins constantly running over at one part towards the sea, although all originally salt, have in the course of time become fresh, because their only supply being directly from the clouds, or from rivers and springs fed by the clouds, is fresh, while what runs away from them must always be carrying with it a proportion of any substance dissolved in them. We thus see how the face of the earth has been gradually washed to a state of purity and freshness, fitting it for the uses of man; and why the great ocean necessarily contains in solution all the substances that originally existed near the surface of the earth, which water could dissolve, namely, all the saline substances. The city of Mexico stands in the centre of one of the most magnificent plains on the face of the earth, 7000 feet above the level of the sea, and surrounded by sublime ridges of mountains, many of them snowcapped. One side of the plain is a little lower than the other, and forms the bed of a lake, which is salt, for the reasons stated above; but the lake will not long be salt, for it now has an outlet. About 150 years ago an extraordinary increase of the lake took place, and covered the pavements of the city; an artificial drain was then cut from the plain of Mexico to the lower country external to it, about sixty miles from the city. This soon freed the city from the water; but, by becoming every year deeper, from the wearing effects of the stream, which has never ceased, it is still lowering the surface of the lake, is daily rendering the water less salt, and is converting the vast salt marshes which formerly surrounded the city into fresh and fertile fields. The immense continent of Australasia, or New Holland, (larger than Europe,) is supposed by some to have been formed at a different time from what is called the old world, so different and peculiar are many of its animal and vegetable productions; and the idea of a later formation receives some countenance from the immense tracts of marshy or imperfectly drained land which have been discovered in the interior, into which rivers flow, but seem not yet to have worn down a sufficient outlet or discharging channel towards the ocean."-Arnott's Physics.