84 Cincinnati Society of Natural History. 



prevent the slipping of the embankment down the hill. The hill 

 upon which Fort Ancient is located is partly of glacial formation 

 and partly limestone. Soil of this nature, when very wet, is apt to 

 form land-slides ; hence, the precaution taken by the builders of 

 the earthwork. 



The total distance round the fort wall, as obtained by very care- 

 ful survey, is 18,712 feet; the shortest distance in a straight line 

 from the extremity of the Old to that of the New Fort, is 4,992 

 feet. The area enclosed within the fortification is about one hun- 

 dred and twenty-one acres. Thus it will be seen that while the 

 embankment does not cover a great space or inclose a great area. 

 it is so tortuous in extent as to measure nearly three and two- 

 third miles. 



Surrounding the fortification on all sides are artificial terraces, 

 which have been, at a great expense of labor, cut into the sides of 

 the ravine. These are one hundred and thirty-two feet above low 

 water mark of the Little Miami River, and are about twenty feet in 

 width. These terraces extend, in some places, for fully half a mile, 

 and the regularity that they display is certainly remarkable, and it 

 is not possible that they could have been formed by natural causes. 

 It may be of interest to the geological readers of this report to here 

 give my reasons for supposing that these terraces are undoubtedly 

 artificial. The plateau on which Fort Ancient is situated is part of 

 glacial formation and part limestone. Opposite the fort the valley 

 of the Miami is very broad, but above and below it narrows. Just 

 below the fort, the hills on each side come within two hundred 

 yards of each other, thus almost shutting in the valley above. In 

 glacial times the hill extended clear across the valley and made a 

 large and deep lake. It is said by those who are considered 

 authority on glaciology that there were many icebergs and cakes of 

 ice floating about in this lake carrying much gravel and masses of 

 rock. These bergs, driven by winds and directed by currents, 

 drifted to the western side of the hill and there stranded, and 

 remained until they melted, and thus deposited the masses of stone 

 and gravel which they carried. So the hill, from about two- third* 

 of the way up, down to the bottom, is nearly all gravel. Since it 

 was deposited, ravines have cut their way through this gravel and 

 the water has washed much of it out into the river below, and the 

 hill presents an irregular appearance, there being nicely rounded 

 knolls of gravel here and there, but no regular layers can be traced 



