| | | 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. | | | | [18] Archæologia Americana, Vol. I. The plan of the Marietta | | Inclosures is a reduction of a part of the survey made in 1837 | | by Mr. Charles Whittlesea, and published by the Smithsonian | | Institution in 1848. | | | | [19] Fort Du Quesne was built about the year 1752. It was | | situated near the spot where is now the town of Pittsburgh. In | | 1731 the Indians who then occupied the lands near Marietta formed | | an alliance with the French, and obtained their assistance in | | protecting them from the attacks of hostile tribes. These were | | probably the Iroquois, who at that period had made a treaty with | | the English, and were their allies during the wars against the | | French in Canada and this part of North America. | | | | [20] Archæologia Americana, Vol. I. | | | | [21] See Plan. | | | | [22] Upon an examination of the map it will be seen that the | | Serpent is placed in the territory west of the Scioto, and that | | the Alligator is east of that river. | | | | The mouth of the serpent is described as being opened wide. This | | peculiarity is observable with the serpent carved upon the walls |