W K K S OK D E F E N (' E 



19 



1843. One or two slight additions have been made to his map, to indicate features 

 which may be of some importance in a consideration of the work and its character. 

 The description of Prof. Locke, accompanying the map, though brief, and 

 written with a view to certain geological questions, may not be omitted in this 

 connection. 



" 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 embank- 

 ment of unusual height and perfection. Meandering around the spurs, and re-enter- 

 ing 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 embank- 

 ment 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 l)uilt is not easily 

 penetrated by water. The bank has been, and is still, mostly covered by a forest 



