464 



MOUND EXPLORATIONS. 



the survey along the top of the wall, and the circular dotted line the 

 nearest approximate circle. Great care was taken in making the sur- 

 vey, and the plat and calculation were found to confirm the accuracy 

 claimed. 



Measuring the various diameters, the maximum is found to be 1,059 

 feet and the minimum 1,050, the mean of which is 1,054.5 feet, but it is 

 found by trial that the nearest approximate circle has a diameter of 

 1,051 feet. The widest divergence between the line of the survey and 

 the circumference of the true circle is 4 feet. 



The aggregate length of the chords surveyed is 3,301 feet, while the 

 circumference of the approximate circle is 3,311 feet; adding to the sum 

 of the chords the additional length of the arcs they subtend (0.1508 of 

 a foot to each 100-foot chord) we have a total of 3,.309 feet. It is there- 

 fore evident that the inclosure approaches, in form, very nearlj' an abso- 

 lute circle. The area including the inner half of the wall is 20 acres, 

 but of the interior level area it is only 18.6 acres. 



This inclosure, which is connected with the "Observatory Circle" 

 according to resurvey, is shown in PI. xxxrii. The southern portions, a 

 to b, and h to o, remain almost uninjured, being still more or less covered 

 by the original forest growth. The other lines of wall have been con- 

 siderably worn by the plow, though they are still quite distinct, the 

 height not being less at any point than 2^ feet, as shown by the figures 

 of the field notes. Nevertheless the wearing makes it difficult, often 

 impossible, to determine with absolute certainty the middle line, though 

 there is never any good I'cason why the survey should vary from the 

 middle line of this, or any other of these Ohio inclo.sures distinctly 

 traceable, more than 3 feet at most. 



The field notes of the survey are as follows: Commencing at station 

 No. 36 (so numbered in the survey of the Observatory Circle) at the 

 point where the northern parallel joins the Octagon; thence to station 

 37, the point where the southern parallel joins the Octagon ; thence to 

 b and round to the place of beginning. 



