the mortuary statistics of Mobile, we shall extract some valuable matters in the next number of the Review. It is impossible for us to do justice to them now. We must also omit any notice of the excerpta and miscellanies, the notices of medical colleges and medical publications, appended at the end of the volume.

May Dr. Fenner find, from the evidences of public favor which shall crown his labors, that he has performed a good work, and one which will add materially to his professional reputation and fortunes.

ART. VIL-SUBMERGED LANDS.

WHICH IS THE BEST AND CHEAPEST METHOD OF RECLAIMING THE SUBMERGED LANDS OF LOUISIANA?

SEVERAL plans have been suggested. One is to straighten the river, and so increase the velocity as to enable the current to dig out a channel sufficient to discharge the waters brought in by its numerous tributaries.

Another is to open new outlets into lake Pontchartrain, and thus discharge the water.

Another is to make embankments of sufficient hight and strength to confine all the water within the channel, and thus prevent overflow.

Professor Robinson, in his able treatise on mechanical philosophy, has deduced, from numerous experiments, made at great labor and expense, by men of practical science, a "Theory of Rivers," which reduces the whole question to a very simple proposition.

He says: "We learn, from observation, that a velocity of three inches per second, at the bottom, will just begin to work upon fine clay, fit for pottery, and, however firm and compact it may be, will tear it up: yet no beds are more stable than clay, when the velocities do not exceed this; for the water soon takes away the impalpable particles of fine clay, leaving the particles of sand, sticking by their lower half, in the rest of the clay, which they now protect, making a permanent bottom, if the stream does not bring down gravel or coarse sand, which will rub off this very thin crust, and allow another layer to be worn off. A velocity of six will lift fine sand; eight will lift sand as coarse as linseed; twelve inches will roll along fine gravel, twenty-four inches will roll along round pebbles an inch in diameter, and it requires three feet per second, at the bottom, to sweep along shivery angular stones, the size of an egg. See p. 466, vol. ii.

We learn, from the same authority, that the velocity of a current depends upon certain fixed laws, which have, in like manner, been ascertained by numerous experiments. He tells us, page 452, on the authority of Mr. Watt, that a canal, eighteen feet wide on the surface, seven feet at bottom, and four feet deep, with a slope of four inches in a mile, has a velocity of seventeen inches per second on the surface, ten at bottom and fourteen in the middle. On the next page he tells us that the velocity of the Po Grande, whose breadth is seven hundred and fifty-nine feet, and depth thirty-one feet, with a declivity of six inches per mile, is thirty-one inches per second, and that the current of the Rheno, whose breadth is one hundred and eighty-nine feet, and depth nine feet, with a declivity of fifteen inches in the mile, is forty-four inches per second.

He shows that the velocity of the current is continued, on a smaller slope, as the rivers, increased by the addition of tributary streams, approach the

sea.

This continued velocity he terms the "energy of deep waters;" and, on pages 476, 477, says:

We have seen in what this energy consists; it is only a greater quantity of motion, remaining in the middle of a great stream, after a quantity has been retarded by the sides and bottom; and we clearly see that, since the addition of a new, and, perhaps, an equal stream, does not occupy a bed of double surface, the proportion of the retardations to the remaining motion must continually diminish as the river increases by the addition of new streams. If, therefore, the slope were not diminished, the regimen would be destroyed, and the river would dig up its channel. We have a full confirmation of this, in the many works that have been executed on the Po, which runs with rapidity through a rich and yielding soil. About the year 1600 the waters of the Panaro, a very considerable river, were added to the Po Grande, and, although it brings along with its freshes a vast quantity of sand and mud, it has greatly deepened the whole Tronco di Venezia from its confluence to the sea. This point was clearly ascertained by Manfredi, about the year 1720, when the inhabitants of the valleys adjacent were alarmed by the project of bringing in the waters of the Rheno, which then ran through the Fenarese. Their fears were overcome, and the Po Grande continues to deepen its channel every day, with a prodigious advantage to navigation; and there are several extensive marshes which now drain off by it, after having been for ages under water; and it is to be particularly remarked, that the Rheno is the foulest river, in its freshes, of any in that country."

Professor Robinson adds: "We insert this remark because it may be of great practical utility, as pointing out a method of preserving, and even improving, the depths of rivers, or drains, in flat countries, which is not obvious, and rather appear improper; but it is strictly conformable to a true theory, and the operations of nature, which never fail to adjust everything, so as to bring about an equilibrium."

It will be seen that this "theory" applies to the Mississippi river. In its character it is like the Po, and it follows, that, as the effect of the introduc tion of two additional rivers, of nearly equal volume, has been to deepen the channel of the Po, greatly for the advantage of navigation, and that, instead of causing it to overflow its banks, it has drained off large marshes, which had been, for ages, under water; so, instead of causing it to overflow embankments confining its waters within its channel, would cause the Mississippi to increase its energy, and thus deepen its bed.

From the mouth of the Ohio to the Balize is a continuous delta, exhibiting the same phenomena which is fully explained by Professor Robinson's theory. It requires a velocity of eight to twelve inches per second to lift and take along coarse sand, whereas a velocity of three inches will lift and carry forward fine clay; thus, as the river approaches the sea, and the velocity of the current is diminished, the coarser particles, held in suspension, are deposited, and the lighter clay is carried forward to the gulf. As the whole delta has been reclaimed from the ocean by the same process, it follows that the lower part of the formation, that is, the particles carried forward to the gulf and deposited, from the bottom to the surface of the water, are chiefly particles of fine clay; and hence we find that the soil, at and below New Orleans, is made of fine, impalpable particles of clay, because, in obedience to a fixed law, the river has deposited the sand and heavier particles above, carrying forward the lighter clay to the gulf. We can now well see why it is that the channel is not more than twelve or eighteen feet deep at the Balize, and not more than ten or twelve at the mouth of the Ohio, and yet is more than two hundred feet deep from Fort Jackson to New Orleans. At the Balize the current is arrested by the waters of the gulf, and the velocity is not sufficient to lift the fine particles of clay deposited in the bed. At the mouth of the Ohio, and above, the velocity is such

that it sweeps along coarse sand, which is deposited before it reaches New Orleans, where the current, although the velocity is not sufficient to take along coarse sand, has the power to lift and carry forward the fine, impalpable particles of clay, which constitute the whole bed of the river at and below the city.

These principles being established, it follows that, if we straighten the river, the velocity will be so much increased that the current must bring down great bodies of coarse sand, which will be deposited in the channel, which, in the first place, would be cut down much below what it now is, and then filled up by the large deposit of heavy sand brought from above, the effect would be to divert the channel into the softer material, on one or the other side of the river, which, in obedience to the laws that govern its course, would cut for itself a meandering bed. It is, therefore, impossible to confine the river within a straight channel: and if it were possible, the current would be so rapid as to prevent its navigation until it brings down so large a deposit of coarse sand as to elevate the bed, so as to give the channel a meandering course. The same results would, in a corresponding degree, be produced by opening one or more outlets into the lake above New Orleans, The volume of water which is now discharged into the gulf, through a channel of one hundred and sixty miles in length, would, in that case, be discharged into the lake, on the same level with the gulf, through a channel of five miles in length, and there would necessarily be a corresponding increased velocity. This new channel would be made through the deposits of fine clay, similar, in all respects, to the fine clay which constitutes the bed of the river at and below New Orleans; and it requires no argument to show that, if the current, with its present velocity, has dug a channel two hundred feet deep at New Orleans, the power of the current, in the new channel, would be such as to turn the whole river into lake Pontchartrain. In that case, the present bed of the river, below the outlet, would soon become a lake, and the communication between New Orleans and the Mississippi river, and between New Orleans and the sea, be cut off by the filling up of both ends of that great lake.

So much, as to the effect to be produced on the city of New Orleans by a new outlet. It remains for us to see what effect this new outlet would have on the channel. As the land rises above the waters of the gulf, it produces, first, grass, then a growth of cane and willows; as we proceed up the river we find cane, and large trees and under-brush, with, in many places, a thick growth of rushes; the grass, rushes, cane and undergrowth, lining the shores of the river, act as filterers, and, by arresting the flow of the current, causes whatever is held in suspension to be deposited at, or near, the bank of the river. At the mouth the deposit is fine clay, further up it is coarse sand.

This deposit, thus made, has raised the banks of the river, whilst that which lies back from it, remains as it was first formed, slightly increased by the deposit of the light particles borne by the overflowing water through the vegetable filterers on or near the banks. We have seen that a velocity of eight inches per second will lift coarse sand-we know that as the current, acting under like circumstances, produces the like effect, the time must have been when the bed of the river at New Madrid was as deep as it is now at New Orleans, yet it is not now, in low water, more than an average of ten feet at and above New Madrid, whilst it is near or quite two hundred feet deep at and below New Orleans, and we now see why this is so; the strong current from above has brought down so much coarse sand as to fill up the bed of the river once as deep at New Madrid as it now is at New Orleans, by filling up the channel with sand so coarse as to resist its further action; each successive overflow has carried the coarser sand and lighter clay into the back lands, until they too have been elevated in a corresponding degree. It follows, that, if we open an outlet into the lake,

and thus produce a corresponding increased velocity in the current above, the river will dig out its bed, and bring down large deposits of course sand, filling up the lake first, and then the bed of the river, until it will have established for itself precisely the same regimen that it now haswhen it will overflow its banks precisely as it now does. It follows, that opening a new outlet is a temporary expedient, which, by increasing the velocity of the current, will bring down the coarse sand much more rapidly and thus fill up the bed of the river with a permanent material, when the overflow will be as great as it now is, unless the current, driven by the resistance of this heavy sand, deposited in the channel, shall cut for itself new beds in the lighter clay. In that case the river will resume a meandering course and no one can tell where it may go.

It remains for us to see what the effect of embankments will be, and here the facts cited by Professor Robinson, that the addition of two streams of nearly equal volume (one in 1600 and the other 1720), instead of filling up the bed or causing it to overflow its banks, has deepened the channel of the Po, and drained large marshes which had been for ages under water, seems to be conclusive; but a matter of so much importance, affecting the interests of so many individuals, should be carefully examined in all its bearings.

We have seen that Professor Robinson's "Theory of Rivers" rests upon a few fixed, known laws; we know that the overflow depends upon the capacity of the channel; we have seen that the channel, at New Madrid, which was once two hundred, is now but ten feet deep in low water, and we now know that this channel has been reduced to ten feet by heavy sand brought from above by an increased velocity of the current, and it requires no argument to show that, as the channel of the river from the mouth of the Ohio to the Balize is one inclined plane, and the velocity of the current depends upon the declivity, that velocity must be increased if we diminish the length of the plane, and that there will be a corresponding diminished velocity if we increase the length of the plane. To open an outlet above New Orleans would diminish the length of the plane, and, by increasing the velocity, bring down the heavy sands now deposited in the upper part of the river; whereas, by elevating the banks and confining the whole volume within the same channel, we would increase the length of the plane and at the same time enable the current to cut out for itself a deeper channel, and by arresting the velocity of the current above, cause the heavy sands to be deposited sooner than they now are, thus arresting the present process of filling up the upper bed of the river at the same time that we deepen its channel; which accounts for the striking facts, cited by Professor Robinson, that the Po, increased by two additional streams of nearly equal volume, each bringing down large quantities of sand and mud, has continued, for more than one hundred years, to deepen its channel, and has drained off large marshes which had been for ages under

water.

The next question to be considered, if we elevate the banks so as to confine all the water within the channel, is, from whence we are to obtain the earth? for we know that the river establishes for itself a regimen, and that a very slight disturbance of the bank may cause an alteration in the current sweeping away large tracts of land. We have a ready answer to this question. The river is constantly bringing down deposits of sand and clay, which may be raised by machinery, driven by powerful steam-engines, and, by a process which I have patented, carried at very little cost to the place where it is to be deposited, and this process has this advantage, that its capacity is equal to any power of steam which may be used. DUFF GREEN.

ART. VIII-MISSISSIPPI VALLEY.

REMARKS ON THE IMPROVEMENT OF THE RIVER MISSISSIPPI-CUT-OFFS.

THERE appears to be an impression on the minds of many, that a cut-off, made through the narrow neck which separates two bends of a river, to shorten by straightening its course, increases the danger of overflow by the accumulation of water in the reach below, supposed to be caused by the too rapid influx of the water from above through the new channel.

This impression is incorrect, entirely unsupported by the authority of experience, and can only be attributed to the difficulty, which most persons find, in arriving at a clear comprehension of the plainest principles of a science with which they have had neither the opportunity, nor the leisure, to become acquainted. Cut-offs have been too often resorted to as an improvement, and with complete success, to permit such an objection to retain any weight.

It will be readily admitted that a straight course of a river, and of proper breadth, by admitting a greater and more uniform velocity, and offering less resistance to the water, causes, all other things being equal, a regular, unchangeable channel; while the winding course, having the line of the current, and greatest depth at the concave bank by producing abrasion of the same, offering increased resistance, and thereby checking the velocity, causes an irregular and continually changing channel. The object of a cut-off is to produce the former, and avoid the latter effect. It sometimes becomes absolutely necessary to resort to a cut-off, in order to relieve the reach above from inundations, which are caused, in time of flood, by the accumulated water, kept back by the obstructions to the free discharge in the channel round the bend.

A cut-off cannot be injurious to a river, if made judiciously, and in accordance to the course of the upper and lower reach of the river. It cannot increase the danger of overflows, for many reasons:

The quantity of water, discharged by a cut-off into the reach below, is just the same that it had previously received round the bend, and, though it may enter with an increased velocity, it soon communicates a share of that velocity to the water there, which, unless kept back by some obstruction in front, will hasten to seek its level further down.

The fall of the surface of the water in the reach below, of course, is not affected by the cut-off. That still remains the same, and, therefore, retains the same power to relieve itself that it had before.

The quantity of water remaining the same, and the fall not being altered, the transporting power of the current is certainly not diminished, but, on the contrary, increased by the additional impulse, communicated to it by the more rapid influx through the cut-off. An elevation of the bed cannot, therefore, take place, to produce a greater vertical rise of the surface.

The height of the surface of the water, in a river, is generally affected by the character of the channel through which it flows. Where the river is obstructed in its course by a bend, or a sudden contraction of the channel, not having sufficient vent, and the velocity being checked by the obstacle in front, the water accumulates above, and its surface rises above its ordinary height. On the other hand, where the channel is open and clear, with no obstacle in front to check the current, it would require an extraor dinary influx from above to cause even a slight rise in the surface of the river; for the increased velocity, communicated to the water below by the high water from above, increases the scouring power, deepens its channel, and causes it to run off too rapidly to admit of its rising very high. Hence it is, that the impulse given to the water in the reach below, by the increased velocity of the influx from a cut-off, is sufficient to deepen the channel and preserve a uniform inclination of the surface of the water.