an extensive accumulation of water, wholly surrounded by land, and having no direct nor immediate communication with the ocean or with any seas, or having so only by means of rivers. Lakes are of various kinds, and have been divided into two classes, according to their situation and causes of production. Those which are formed in deep hollows between the ridges or at the bases of mountains, and which are supplied with water by springs or torrents, are classed together; and those which are formed in low and level countries by the surplus water of rivers, or from a want of sufficient declivity in the ground to allow the waters to continue their course, constitute a second class. But there are several other characteristics belonging to lakes, which justify a more minute division; and four distinct kinds have been recognised. The first class comprehends those which have no issue, and into which no running water flows. These, being generally diminutive in size, do not merit much attention. Some of them, as the Arendt, in Vieille Marche, are formed by the sinking down of the circumjacent lands; others, like the Lake Albano, near Rome, appear to be old volcanic craters filled with water. The second class consists of those lakes which discharge, but receive no running water. These are formed by springs, which, rising in a hollow place or reservoir, fill it before they find an outlet for their own waters. These lakes, however, are fed by small, almost invisible, streams, which descend from contiguous heights, or from subterraneous canals. Lakes of this description are often the source of large rivers, and they are naturally situated on great elevations. There is one of this kind on Mount Rotondo, in Corsica, which is 9294 feet above the level of the sea. The third class, consisting of lakes which receive and discharge streams of water, is very numerous. Each of these lakes may be considered as a large basin or reservoir for receiving the accumulated waters of the neighbouring countries. They have in general only one opening, which almost always takes its name from the principal river which flows into it. These rivers are sometimes said to traverse the lakes; but this is scarcely correct, as their waters mingle with those of the basin over which they are diffused. These lakes have often sources of their own, either near the borders, or in their bottom. There are four or five lakes of this class in North America, which in magnitude resemble seas, but which preserve their clearness and sweetness notwithstanding, by the flow of a continual stream of fresh water. Sometimes a chain of lakes are connected with one another and with the ocean, by a series of rivers. This is the case with the great lakes on the northern frontier of North America, where basin succeeds basin on a lower level, like so many locks of a canal.

A fourth class of lakes are those which receive streams of water, and often great rivers, without having apparently any outlet. These lakes are in general confined to warm climates; but the Caspian Sea, the largest of all lakes, belongs to this class. (See the article on the Caspian Sea.) There are a great many others besides in Asia; and South America contains the Lake Titicaca, which has no efflux, although it receives very considerable rivers into it. Such lakes appear to belong to the interior of great continents; they are placed on elevated plains, which have no sensible declivity towards the sea, and which do not allow of the water opening for itself a passage through which to flow out. It was long conjectured, that, by some subterraneous channel, lakes of this description communicated with the sea; but the fact that the surfaces of some of the most remarkable of them, such as the Caspian and the Dead Sea, are depressed below the level of the ocean, is quite sufficient to explode this hypothesis. For were there any communication, however small, the ocean would flow into the lake till it brought it to a level with itself. The true explanation seems to be, that a quantity of water equal to that which runs in is carried off by evaporation. The absorption of liquid by the contiguous land may also materially assist in carrying off the surplus fluid.

There is another class of lakes, which differ materially from any of the preceding, namely, those which are contained in cavities quite covered over by earthy strata. These are probably very numerous, for it frequently happens, that after any violent convulsion of the globe, such as an earthquake, they become exposed to view; and, by the operations of mining, digging of wells, and the like, they have often been met with. Some of them appear to be the source of rivers, whilst others are known to receive very considerable streams, which lose themselves in the interior. Such are the numerous cavities of the Julian Alps. Certain lakes situated above ground periodically disappear; and their waters, it is most probable, flow into similar reservoirs. That very extensive subterranean cavities exist, is sufficiently attested by numerous phenomena. The disappearance of rivers, the waters thrown up by volcanoes, the sudden and terrible inundation of mines, the mountains which are suddenly engulfed in the bosom of lakes, and the springs of fresh water which spout up in the midst of the ocean, are all so many evidences of the fact. There is a district in the interior of Algiers, where the inhabitants, after digging to a depth of about two hundred fathoms, invariably come to water, which flows up in such abundance that they call it the subterranean sea.

The physical phenomena which certain lakes present are very remarkable, and were calculated to excite astonishment in an age when the operation of natural causes was not sufficiently attended to. Periodical lakes are the most common. Those which are formed by excessive rains, and which are evaporated by solar influence, are sometimes of great magnitude, as in tropical climates, where they cover spaces of several hundred leagues in length and breadth. Towards the poles they shrink into mere pools, scarcely worthy of notice. But there are lakes entirely independent of the rainy season, which appear and disappear at certain intervals, although these changes do not seem to take place at regular intervals. With regard to such sheets of water, Malte-Brun observes: "If there exist now in the numerous cavities of the earth subterraneous lakes of this kind, and if these communicate with other lakes which are visible, it is easy to imagine that the waters of these last may sometimes entirely disappear, by sinking down into the basin of the subterraneous lakes in proportion as they dry up. This lower basin again filling itself anew, the waters issue from it to fill the superior basin. If, in a supposable series of subterraneous cavities, the last link of the chain happen to be a mass of subterraneous water, situated at an elevated level in the bosom of a mountain, the periodical return of the waters in the visible basin may be accompanied by a motion similar to that of the spouting fountains. It is by means of such hydraulic machinery that nature keeps up the wonders of the lake of Cirkinitz in Illyria, and in many others of the same description."

There are some lakes which present very remarkable phenomena, such as rising and falling like a tide, and boiling, and becoming agitated even during serene weather. Some of the Scottish lakes, and the Welter in Sweden, often experience violent commotion when the atmosphere is perfectly still. It seems highly probable that these agitations are connected with earthquakes in distant countries; and a coincidence in dates on certain occasions has given countenance to this belief. In Portugal there is a small lake or pool near Beja in Alemtejo, which emits a loud noise on the approach of a storm. Other lakes appear agitated by the disengagement of subterranean gases, or by winds which blow in some cavern with which the lake communicates. Near Boleslaw, in Bohemia, there is a lake of unfathomable depth, which sometimes in winter emits blasts of wind so strong as to elevate to some height ponderous pieces of ice. In the Marche of Brandenburg, the pool of Krestin often commences in fine weather to boil up in whirlpools, so as to engulf small fishing boats.

With regard to depth, lakes vary infinitely. In those situated in mountainous districts, it is remarkably great; that of Lochness, in Scotland, is one hundred and thirty fathoms in some parts. The general depth of the Caspian Sea is from sixty to seventy fathoms; but this increases towards the southern end to such a degree that no bottom can be found with a line of three hundred and eighty fathoms. The lake of Geneva attains the great depth of one hundred and sixty-one fathoms, and there are many others known to be exceedingly deep, without the amount being exactly ascertained. Several have passed for ages amongst the vulgar as bottomless; but this opinion, it is scarcely necessary to say, is unworthy of credit. Yet we are not to reckon as fabulous the accounts of lakes with double bottoms, which are said to be found in Sweden and elsewhere. This phenomenon is supposed to arise from interwoven roots becoming incrusted, and, being suspended near the bottom of a lake, rise and fall according to circumstances, thus causing the depth to vary in appearance.

In regard to the temperature of lakes, see the article Climate. Distinct from any of the characteristics of lakes yet alluded to, is the chemical nature of their waters. Lakes, in respect to the quality of the waters, are distinguished into fresh, saline, and alkaline. Those which receive and discharge considerable quantities of fresh water are almost always kept themselves in a state of perfect freshness; but those which have no outlet are invariably saline. Thus the Dead Sea, whose waters have no efflux, and into which the river Jordan continually flows, contains about eight times as much salt as common sea-water. The waters of the Jordan are brackish, and the neighbouring soil is much impregnated with salt, so that the accumulation of such a quantity of saline matter in the lake, during a series of ages, is by no means surprising, for none of it ever passes off by evaporation. Salt must likewise be accumulating in beds at its bottom; for as soon as water is perfectly saturated, and can hold no more salt in solution, the latter must fall to the bottom. Some of the large Asiatic lakes are dried up during summer, and their beds appear lined with an incrustation of salt. All the great American lakes consist of fresh water; those of Europe are either fresh or slightly saline; but the Caspian Sea, and various others which are situated in plains full of salt, or in tracts of country where salt springs abound, are almost invariably impregnated with that substance. Some lakes are both saline and alkaline, as is the case with the Natron Lakes in Lower Egypt. They derive their appellation from their abounding in soda, which is there called trona and natron, the nitre of the Scriptures. Some lakes produce a pitchy substance. In the island of Trinidad there is one, on the surface of which an enormous quantity of bitumen, fit for naval purposes, is collected. Deposits of various kinds, besides those enumerated, seem to owe their origin to lakes. Bog iron-ore, or hydro-phosphate of iron, is often found in such situations as to show that it has been deposited from the waters of lakes; and in some countries it is collected from the sides and bottoms of lakes once in a certain number of years. Calcareous springs are numerous, and when the waters of these collect in a hollow place, so as to form a lake, quantities of calcareous sinters and tufas are deposited, so that the lakes when emptied present extensive deposits of that mineral. The travertine employed at Rome for building is a lake or spring calcareous deposit of sinter and tufa.

From the great changes which have been taking place for a series of ages, the number, the extent, and the situation of lakes must have from time to time been materially altered. That they occupied a greater extent of the earth's surface formerly than they do now, is quite consistent with geological phenomena. But the investigation of the subject belongs more properly to Geology, which see under the head of Mineralogy.

Lacque, a preparation of different substances, which are formed into a kind of magistery for the use of painters. One of the finest and first invented of these was that of gum lacca or lacque, from which all the rest, as made by the same process, are called by the common name lacques. See Lacca.