Note 17 — Chapter IV · ANCIENT INDIAN MOUNDS AND EARTHWORKS IN OHIO. Earthworks of the Mound Builders and their geographical position.—Miamisburgh Mound.—Grave Creek Mound.—Ages and contents of burial mounds.—Rectangular, circular and octagonal Inclosures near Newark.— Marietta Earthworks.—Discoveries made in a burial mound.—Fortifications near Portsmouth.—Encampments in the valley of the Scioto.
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I have seen a re-survey of the Newark inclosures made on behalf of the Smithsonian Institution, under the direction of Professor Cyrus Thomas. The results of this survey are very useful. The measurements have evidently been taken with much care. With respect to the Octagon, Professor Thomas observes that, “The angles at the crossings of the diagonals and diameters at the centre O, are so nearly right angles as to be worthy of notice in this connection. For instance, the angles at the crossings of the diagonals BF and DH, differ but 10´ from true right angles, while those at the crossing of the diameters AE and CG differ but 2´.”
As regards the Square he states, that, “This inclosure varies but slightly from a true square, the course of the opposite sides in one case differing but 31´, and the other but 6´. The greatest variation at the corners from a true right angle is 57´.”
The large Circle D is said to have a difference of diameters of twenty-six feet, these being respectively 1189 feet and 1163 feet.
The Observatory Circle, which is the inclosure connected with the Octagon, was found to have been made with remarkable correctness. “The widest divergence between the line of the survey and the circumference of the true circle is four feet. It is therefore evident that the inclosure approaches in form very nearly an absolute circle.”
Professor Thomas also states with reference to the Observatory Circle, that the radius is almost an exact multiple of the surveyor’s chain.
The geometrical accuracy of the lines of embankments and of the inclosed areas in earthworks of such great dimensions, covering such large spaces of ground, is not the least strange fact concerning these works.