In the year 1164, a violent storm of wind caused a deluge in Friesland, which occasioned the death of many thousand persons. In 1218, another inundation in Friesland occurred, by which 100,000 persons were drowned ; and another equally destructive took place in 1530. Florus speaks of a rising of the water in the year of Rome 644, which forced the Teutonians, Cim brians, and Tigurians, back from the countries they in habited. This was occasioned by a violent north wind, which raised the ocean along the coast of the countries they inhabited.
Water in the state of ice, also produces considerable changes on the surface of the earth. Thus we often observe masses from a hundred weight to many tons floated by rivers during thaw•fLods, and these frequently break up the banks of the rivers, and even tear away immense masses of solid rock. Sea-ice also produces vftlflar effects on coasts, but on a greater scale.
It sometimes happens, that great fields of ice rise from the bottom, and bring with them masses of rock several hundred tons weight. These masses of stone are embedded in the ice. They are carried along with the ice, and deposited on shores at a great distance from their original situation. This fact will serve to explain the appearance of loose blocks of particular kinds, in situations far removed from their original re pository.
Similar changes are occasioned by the fall of ice front the heights of mountains. When the glacier, or moun tain ice, rests on inclined planes, dreadful devastation is caused by it, during the time of floods, as it then splits, and is hurled down to the lower country with irresistible impetuosity. The inhabitants of the Alps of Switzerland and Savoy, of Iceland and Greenland, often experience the terrible effects of the fall of these tremendous Ill a SC s.
In like manlier, the fall of snow produces striking ef fects. The consolidated snow is often precipitated with great velocity, accompanied with terrible noises, carrying along with it rocks of vast size, and often burying vil lages under it.
The freezing of water contained in the fissures of rocks also occasions considerable alterations on the sur face of the earth. This is observed most particularly in those rocks that have perpendicular fissures, because these allow the water to enter more easily, and favour the separation of the masses when the water expands doting the process of freezing. Hence we find no spe cies of rock more changed by the effects of frost than basalt and porphyry-slate.
The Chemical effects of water, particularly the de stroying effects, depend on the kind of rock over which it flows ; for some allow water to act on them chemi cally, others do not. Limestone, gypsum, and rock-salt, are more particularly acted on by water than most other rocks.
By this agency of water, the height of limestone and gypsum mountains is gradually diminished, caves are excavated in them, and the water of such countries is much impregnated with gypseous and calcareous mat ters. The rock-salt which occurs in hills of gypsum is often dissolved by the water, and thus cavities of con siderable magnitude are formed ; and by the continued action of the water on the gypsum, the cavities increase in size, until the superincumbent pressure becomes too great, and then the roof falls in and forms those re markable funnel-shaped hollows so often observed in gypsum countries.
Sometimes, as in felspar rocks, the percolating water washes away the alkaline ingredient ; in other casts, the moisture combines with iron, and forms hydrate, or by its decomposition oxidates the metallic substances in a greater or less degree. By its action on sulphurous compounds, as on pyrites, it gives rise to sulphates or vitriols. As iron is the most general and abundant metal in the mineral kingdom, and is easily acted on by air and moisture, it follows that it must be one of the most active agents in the disintegration of mineral substances.
Forming Effects of Water.
We shall next consider the forming effects of water, which are, as already mentioned, either mechanical or chemical.
It is evident, that every mechanical destruction will be followed by a mechanical formation ; for the masses which are separated by the water will be again deposit ed on the surface of the land, in lakes, rivers, on coasts, or on the bottom of the sea. During land floods, the water does not always convey its mechanically mixed parts to rivers ; on the contrary, it often deposites them in hollow places. Those particles that reach rivers form sand-banks, particularly in slow-flowing rivers. Very extensive mechanical formations are daily taking place on the coasts, and even in some places at a con siderable distance from them, by the waters of the ocean. In the Baltic or East S. a, many appearances of this kind are to be observed. Thus the Bay of Fulbaka, which was navigated with boats within the memory of man, is now filled up, and covered with grass. Several har bours in Lapland that formerly admitted vessels, are now three or four thousand paces from the sea; and at Helsingor there are iron-works in places which were covered by the sea about eighty years ago. The whole of the ancient kingdom of Prussia appears to have been formed in this manner ; it is said that the sea reached as far as Culm within the period of human history. The city of Dantzic, several hundred years ago, was close on the sea-shore.