“This work occupies a terrace on the left bank of the river, and two hundred and thirty feet above its waters. The place is naturally a strong one, being a peninsula, defended by two ravines, which, originating on the east side near to each other, diverging and sweeping around, enter the Miami, the one above, the other below the work. The Miami itself, with its precipitous bank of two hundred feet, defends the western side. The ravines are occupied by small streams. Quite around this peninsula, on the very verge of the ravines, has been raised an embankment of unusual height and perfection. Meandering around the spurs, and re-entering to pass the heads of the gullies, it is so winding in its course that it required one hundred and ninety-six stations to complete its survey. The whole circuit of the work is between four and five miles. The number of cubic yards of excavation may be approximately estimated at six hundred and twenty-eight thousand eight hundred. The embankment stands in many places twenty feet in perpendicular height; and although composed of a tough, diluvial clay, without stone, except in a few places, its outward slope is from thirty-five to forty-three degrees. This work presents no continuous ditch; but the earth for its construction has been dug from convenient pits, which are still quite deep, or filled with mud and water. Although I brought over a party of a dozen active young engineers, and we had encamped upon the ground to expedite our labors, we were still two days in completing our survey, which, with good instruments, was conducted with all possible accuracy. The work approaches nowhere within many feet of the river; but its embankment is, in several places, carried down into ravines from fifty to one hundred feet deep, and at an angle of thirty degrees, crossing a streamlet at the bottom, which, by showers, must often swell to a powerful torrent. But in all instances the embankment may be traced to within three to eight feet of the stream. Hence it appears, that although these little streams have cut their channels through fifty to one hundred feet of thin, horizontal layers of blue limestone, interstratified with indurated clay marl, not more than three feet of that excavation has been done since the construction of the earthworks. If the first portion of the denudation was not more rapid than the last, a period of at least thirty to fifty thousand years would be required for the present point of its progress. But the quantity of material removed from such a ravine is as the square of its depth, which would render the last part of its denudation much slower, in vertical descent, than the first part. That our streams have not yet reached their ultimate level, a point beyond which they cease to act upon their beds, is evident from the vast quantity of solid material transported annually by our rivers, to be added to the great delta of the Mississippi. Finally, I am astonished to see a work, simply of earth, after braving the storms of thousands of years, still so entire and well marked. Several circumstances have contributed to this. The clay of which it is built is not easily penetrated by water. The bank has been, and is still, mostly covered by a forest [p020] of beech trees, which have woven a strong web of their roots over its steep sides; and a fine bed of moss («Polytrichum») serves still further to afford protection.”