vations, in consequence of which, rocks are ned and precipitated into their beds. The hus obstructed, accumulates, and cuts for itannel, taking with it an additional quantity of Is manner, also, the stream is often made to rection, perhaps obliquely across the valley h it runs. The unequal hardness of the soil use of change in the direction of streams, and gs of wood, leaves, and other matters with s are often charged. When from these, or a current is made to deviate from its course, vears a curve into the opposite bank, where a moment accumulates, and then receiving rection from the lower side of the curve, to the opposite side, where a similar curve d, and the water made to re-cross the channel "hus we often see brooks and rivers crossing ng the valleys through which they run, many ometimes, after taking a wide sweep, returnrly to the point where the same water had ur, or many hours before. When this hap

DA

pens, and every one has seen such instances, it is often the case that during some overflow of the stream, the water cuts across the isthmus at A, as seen in the diagram, and thus forms an island. In conis, the water not only takes a new direction lar point, but often the foundation is thus laid ble changes below the island.

entine windings, not only take place in trout n the largest rivers, and thus become the elling and fertilizing tracts of country of ss extent. The Mississippi, through a cont of its course, cuts across its immense valley er here described, and sometimes after runventy miles, returns back again nearly to the The fertile valley of the Connecticut has in a great measure by the same means. The 's, now every year irrigated by its waters, rmed in the course of time, by the changes of Es is shown by the logs of wood uncovered

es have been found 20 feet below the present surface s banks.

Roman Republic tome parts of that marshes, have been slow! Parma and Cremona, wh me cause. Since 1390 a part of the territory of mais old channel being name of Po morto, or ell, which formerly sto ar stands on the right anged its locality. I tated that several church ards rebuilt at a greate is devastating stream, a ry pulled down their distance from the Po. To keep this wild stro em of embankment, th aly, was commenced as continually been i The increased velocity eing thus confined, cau Teater quantity of allu because there are deposit the

estinating the transporting power of water, we are o forget its buoyancy, and on which indeed its power oving heavy substances, such as rocks, in a great meadepends. The specific gravity of many rocks is little e than twice that of water, that of granite and limee being about 2.50, that is, two and a half times, bulk ulk, the weight of water. Hence a stone weighing ty-five pounds in the air or under ordinary circumces, will weigh only fifteen pounds when immersed in r. Those who have never tried the experiment of g a stone under water, will be surprised to find, with ease he can raise a block of granite to the surface, e which, however, with all his efforts, he cannot lift it. man can lift a stone weighing one hundred pounds se specific gravity is two, in the air, he can lift one ghing two hundred pounds in the water, because the I lifts just one half of its weight. It is from our not ng this circumstance into account, that we are often sured at the power of torrents to move stones of great size. ccording to experiments recorded in the EncyclopeBritannica, a velocity of water equal to three inches second is sufficient to tear up fine clay,-six inches per nd fine sand-twelve inches per second fine gravel; three feet per second small stones. It is obvious, ever, that the depth of the water will influence these lts, and that the power of moving bodies will be in ortion to its depth and velocity.

ince the time of historical records, the power of run-
water has produced many, and great changes in va-
s parts of the world. In some instances, lakes have
filled in others, deep ravines have been formed,
up,
thers whole districts have been ruined in consequence
ivers having changed their beds, and in others, conside-
e tracts of land have been accumulated, or sometimes
pt away, by the force of mountain torrents.

1

Waters can

e

de Po, even since the m The ancient city of the Adriatic, but it is In the twelfth century, shore, the Po having il since that period. But notwithstanding the sea in consequence deposited in its bed; f the plains during an o arrow limits of its ba deposition, it is More the mud and sa place it on the embar be in danger of brea whole plain below. This system has present day, the Po c tance, on the top of a

Effects of the River Po. The Po affords a grand example he manner in which a great and rapid stream, bears n to the sea, the alluvial matter poured into it by a titude of tributaries, descending from lofty chains of untains. The changes gradually produced by this r in the great plains of Northern Italy since the time

Stant

4

in Republic have been exceedingly disastrous rts of that country. Extensive lakes, and ve been slowly filled up, as those of Placentia, Cremona, while others have been drained by the

Since 1390 the Po deserted its bed through territory of Cremona and invaded that of Parhannel being still obvious, and retaining the o morto, or dead Po. The town of Bresformerly stood on the left bank of the river, on the right, the river, not the town, having locality. In the ancient parish records it is everal churches were taken down and afterIt at a greater distance from the new bed of ing stream, and in 1471 the friars of a monasdown their edifice and erected it at a greater n the Po.

this wild stream within bounds, a general sysankment, through the plains of Northern ommenced in the thirteenth century, which ally been increased until the present time. ed velocity of the river, in consequence of its confined, causes it to transport to the sea a much tity of alluvial matter than it would otherwise there are no sluggish intervals where its deposit their sediment. Hence the delta of since the memory of man, has greatly increasncient city of Adria was originally a sea port tic, but it is now twenty miles from the shore. th century, Adria was about six miles from the Po having added fourteen miles of alluvial at period.

thstanding more alluvial matter is carried into Onsequence of this embankment, more is also its bed; for that which would be spread upon uring an overflow is now confined within the ts of its banks. In consequence of this contion, it is found necessary every year to reaud and sand from the bed of the river, and the embankment, otherwise the water would er of breaking through, and destroying the - below.

tem has been so long continued, that at the the Po crosses its plains to a considerable dis

ton of a high and co tinued mound like the

of rock through which it passes consists of 1 shale, the latter a dark coloured shelly formet thick, lying under the limestone. The 70 feet thick, above which is the ordinary untry.

tone is hard, and lies in horizontal strata at e falls; but the shale is soft, and is acted upon greater facility than the limestone, so that the often overhangs the former perhaps forty feet of the precipice.

s of wind charged with spray, which rise out nto which this enormous cascade is projected, st the shale beds, so that their disintregration and the superincumbent projecting limestone ithout a foundation falls from time to time in ky masses. When these enormous fragments k is felt, often at considerable distances, acby a noise resembling a distant clap of

ers which expand at the falls, where they are he island, are contracted again after their union im averaging not more than 500 feet broad. row channel, immediately below this immense ters, a boat may pass across the stream with he pool into which the cataract is precipitated feet deep, the descending water sinks down and

cent while a sun

edd

the