with water. The second class are those which have an outlet, but which receive no running water. They have been formed by springs flowing into some large hollow upon the water rising up to the top of the hollow, it would, of course, run over the lowest part of the edge, and thus find an outlet, and these outlets are, in some cases, the beginnings of very large rivers. As these lakes receive no stream, they must necessarily, in most cases, be in elevated situations. There is one of this kind on Monte Rotondo in Corsica, which is 9000 feet above the level of

the sea.

The third class, which embraces all those which both receive and discharge streams of water, is much more numerous than any. Though they are the receptacles of many streams from the neighbouring country, they usually have each but one outlet, which often takes its name from the principal river that runs into the lake. The largest lakes of this class are the immense bodies of water in North America, between Canada and the United States. There are five, (Superior, Michigan, Huron, Erie, and Ontario,) almost like seas in extent, connected together, and their purity is maintained by means of the continual flow of water which is kept up from one to another. Their final outlet to the Atlantic Ocean is the great river St. Laurence. Lake Baikal, in Asiatic Russia, is also remarkable for its size; it sends forth a large stream which joins the Yenisei.

The fourth class of lakes comprises a very small number, but they are the most singular in their character of all. They are those which receive streams of water and often great rivers, but have no visible outlet whatever. The most celebrated are the Caspian Sea and Lake Aral, both situated in the west of Asia. The Caspian is between 600 and 700 miles long, and, in one part, between 300 and 400 miles in width; it receives some very large rivers, the chief of which are the Volga, the Ural or Yaik, and the Kur; yet, notwithstanding the plentiful supply of water which is constantly being poured into it, it not only exhibits no increase, but there is strong reason to believe, from the appearances round its shores, that its surface is now much lower than it was at a former period *. Many con

*By means of observations made with the barometer upon the coasts of the several seas, the surface

jectures have been offered to account for this apparent anomaly; but, after all, the process of evaporation seems quite sufficient to explain it, especially when we consider the extensiveness of the surface which this inland sea (as it is termed) presents, to be acted upon by the atmosphere. Lake Aral is much smaller than the Caspian, but possesses the same peculiarities, and, from the character of the isthmus which separates them, it is supposed that they formerly composed one body of water. They are both salt lakes, and are distinguished by marine productions; from these circumstances it has been conjectured that they must, at a very remote period, have been connected with the Black Sea. If such a connection ever existed, the separation may have been occasioned by an accumulation of alluvial soil, brought down by the rivers Don and Volga.

The phenomena presented by some lakes are of a very curious kind. Several of these bodies of water are periodical in their appearance. In tropical countries, owing to the violent rains and the overflowing of the rivers, spaces of several hundred miles are often covered with water. South America has large lakes which are annually formed in this manner, and are again dried up by the powerful evaporation of an equatorial climate. Some lakes there are which periodically appear and disappear, owing (it is thought) to their invisible connexion with some subterranean reservoir, by the alternate increase and diminution of which they are necessarily influenced. Lake Cirknitz in Illyria is of this description. The motions and agitations which certain of these bodies of water experience are more difficult to explain. Some of them appear agitated by the escape of subterraneous gases, or by winds that blow in some cavern with which they communicate. Loch Lomond, in Scotland, and Lake Wetter, in Sweden, are often violently agitated during the calmest weather. The floating islands which exist in several lakes, seem to have been formed by the water first undermining and then detaching from the bank very light earth of the nature of peat; sometimes they are merely reeds and roots of trees woven together. Those of the lake of

of the Caspian was ascertained to be 306 feet below that of the Baltic, and nearly 345 below that of the Black Sea.

Gerdau, in Prussia, are said to yield pasturage for one hundred head of cattle; and in the lake of Kolk, in Osnabruck, there is one which is covered with elm trees.

On the Changes which take place in the
Earth's Surface.-Action of Running
Waters.-Breaking down of Coasts.
-Encroachment of Sands.-Form-
ation of New Islands.-Volcanoes.-
Earthquakes.

FROM the quiet and regular succession
of natural events to which we are accus-
tomed, and the repugnance we feel to
the idea that it is possible for the
course of nature to suffer interruption,
we might, without due investigation,
almost persuade ourselves that the phy-
sical features and condition of the globe
possess an unchangeable character. So
far, however, is this from being the
case, that there is no country wherein
traces are not discoverable of the great
changes and violent revolutions of which
the earth has formerly been the theatre.
The confusion often exhibited in the
position of the different strata or layers
of which the crust of the earth is com-
posed, the frequent discovery of the re-
mains of animals and vegetables deeply
buried in the soil, and many other ap-
pearances, testify that the surface of the
globe has undergone convulsions, to the
production of which none of the natural
agents with which we are acquainted
can be regarded as adequate; unless
they once acted in a method, and with
an extent of violence, of which it is im-
possible for us, by reference to what
now exists, to form a conception. "The
lowest and most level parts of the earth
exhibit nothing, even when penetrated
to a very great depth, but horizontal
strata, composed of substances more or
less varied, and containing almost all
of them innumerable marine produc-
tions. Similar strata, with the same
kind of productions, compose the lesser
hills to a considerable height. Some-
times the shells are so numerous as to
constitute of themselves the entire mass
of the rock; they rise to elevations su-
perior to the level of every part of the
ocean, and are found in places where
no sea could have carried them at the
present day, under any circumstances ;

*

*Fossil shells have been found on the summits of the Pyrenees; and among the Andes as much as 13 and 14,000 feet above the level of the sea.

they are not only enveloped in loose
sand, but are often inclosed in the
hardest rocks. Every part of the earth,
every continent, every island of any ex-
tent, exhibits the same phenomenon."
(Cuvier's Essay on the Theory of the
Earth.) The perfect state in which
these shells are generally found, and the
regularity, thickness, and extent of the
beds that contain them, prove that they
could not have been deposited in their
places by any temporary invasion of
the sea, but that the water must have
remained there long enough in a state
of tranquillity, to have allowed them
gradually to deposit themselves. Some
of the strata of marine formation are
much more recent than others; while
in the midst of even the oldest strata of
this kind, other strata appear full of
animal or vegetable remains of land or
freshwater productions. On these ac-
counts, it would seem as if the land,
now inhabited by man, had experienced
various successive irruptions and re-
treats of the sea. There are also ap-
pearances which lead to the conclusion
that the catastrophes which have occa-
sioned these changes have been sudden
and violent. To numberless living be-
ings, they were the messengers of de-
struction, and of many, the very races
have been utterly extinguished. Cuvier,
the celebrated French geologist and
natural historian, from an observation
of the fossil bones of more than one
hundred and fifty quadrupeds, has de-
termined that upwards of ninety of these
animals were of kinds unknown to na-
turalists. There can be no doubt that the
revolutions in which these animals were
destroyed, occasioned great changes of
climate in many parts of the earth, and
that in some instances, at any rate, the
change took place very rapidly. Fossil
plants, and animals of similar kinds to
some which still exist in warm regions,
have been found in countries where the
cold is very much beyond what such
kinds are capable of sustaining; and in
the arctic zone, the carcasses of large
quadrupeds have been discovered en-
veloped in the ice with their skin, hair,
and flesh, still remaining, so that the
alteration in the climate must have oc-
curred with such suddenness, as to pre-
vent their bodies from being decomposed
by_putrefaction.

Such are some of the traces that bear witness to the revolutions which the surface of the globe has undergone. These wonderful and destructive events,

of the immediate causes of which nothing can be declared with certainty, must have long ceased; but the earth has since experienced, and is still experiencing, changes of a very perceptible kind, which we shall now proceed to notice.

waves, by casting up sand upon them, assist in their increase, whole provinces are created, capable, from their rich soil, of yielding, in the highest degree, to the support of man, and of being made the seats of wealth and civilization.

It has been concluded, with reason, Of the several agents which contri- that the greater part of Lower Egypt bute to these changes, water has the owes its formation to the alluvial matter widest sphere of activity. In all abrupt brought down by the Nile, aided by the and precipitous mountains, fragments sand cast up by the sea. M. Dolomieu of earth and rock are continually falling has endeavoured to show that the down from the higher parts, owing to tongue of land on which Alexandria the slow, but effectual action of rains, was built, (331 years before Christ,) storms, &c.; and these become rounded did not exist in the days of Homer; by rolling upon each other. These frag- (about 900 B. C.,) and that the lake ments collect upon the sides and at the Mareotis was, at the latter period, a foot of the mountains, and, on some oc- large gulf of the sea. In the time casions, when undermined by rivulets *, of Strabo, the geographer, who lived have been known to slip down in im- about the commencement of the Chrismense masses, and by stopping up the tian æra, this gulf had been inclosed by course of rivers, create great devasta- land, and is described as a lake of six tion. But, without any such extraordi- leagues in length. More certainty exists nary occurrences as these, the streams as to the changes that have occurred that descend along the flanks of since that period. The sand thrown up elevated grounds carry along with by the sea and wind has formed, near them some portion of the materials of the site of the ancient town, a narrow their respective slopes, especially when tongue, on which the modern Alexanswelled into violence by rains or the dria stands. It has blocked up the melting of snows; and such as come nearest mouth of the Nile, and reduced from mountains sweep down with them the lake Mareotis almost to nothing; even some of the fragments of rock that while the rest of the shore has been very have been collected in the high valleys. much extended by the continual depoIn proportion, however, as these streams sition of alluvial matter. In the time reach the more level country, and their of the ancients, the Canopian and Peluchannels become more expanded, they sian were the principal mouths of the deposit the fragments and stones, till at Nile, and the coast ran in a straight last their waters convey along only par- line from the one to the other. The ticles of mud of the minutest kind. If, water now passes out chiefly through therefore, these waters do not run too the Bolbitian and Phatnitic mouths; rapidly into the sea, or the particles in and round them the greatest depositions question do not previously settle in have taken place, to which the coast is some lake through which the rivers indebted for its swelling outline. The pass, the mud is deposited at the sides cities of Rosetta and Damietta, which of their mouths, forming low grounds, were built upon these mouths close to by which the shores are prolonged and the sea, less than 1000 years back, are encroach upon the sea; and when the now six miles distant from it. At the same time that the sediment of the Nile occasions an extension of the land, both the bed of the river and the country, which is periodically covered by the overflow of the waters, are, from the same cause, gradually being raised to a greater elevation. As a proof of this elevation of the soil, it is stated that at Cairo, before the rise of the river is

*Large masses of rock have, however, been known to detach themselves, and roll down from mountains

without any apparent cause.

In Mr. Bakewell's Travels, vol. I., p. 195-202, there is an interesting description of the fall of a part of Mont Grenier, in Savoy, which took place in 1248. The ruins spread over an extent of nine square miles, and entirely buried five parishes, and the town and church of St. André. Some of the small hills or rocks, of which the ruins consist, are at the distance of three and four miles from the mountains from which they were separated. This catastrophe, Mr. Bakewell remarks, must have been caused by the gradual decay of the soft strata, of which the lower part of the mountain consists; whereby the mass of limestone above was undermined, and becoming detached, fell with destructive violence into the plain. There are appearances about Mont Grenier which threaten a renewal of the catastrophe of 1248.

The Canopian or westernmost mouth, which used to discharge itself into the sea not far from the site of Aboukir, is now lost in the lake of Etkoo; the Pelusian, the easternmost mouth of the Nile still exists, but in a very insignificant state, flowing through the lake Menzaleh.