The vast number as well as the magnitude of the works found in the State of Ohio, have surprised the most careless and indifferent observers. It is estimated by the most conservative, and Messrs. Squier and Davis among them, that the number of tumuli in Ohio equals 10,000, and the number of enclosures 1000 or 1500. In Ross County alone, 100 enclosures and upwards of 500 mounds have been examined. Some of the works exhibit fine engineering skill; such, for instance, are those near Liberty, Ohio, where two embankments, each forming a perfect circle, are found in conjunction with a perfect square. The larger circle measures 1700 feet in diameter and contains forty acres, while the smaller has a diameter of 800 feet. The square contains twenty-seven acres and measures 1080 feet on each side. One set of works in Pike County consists of a circle enclosing a square, the four corners of which each touch the circular embankment. The opening or doorway through the circle is opposite the opening in the square. Prof. E. B. Andrews found a conical mound enclosed by a circle, the base of the mound reaching to the edge of the ditch outside of which is the circular wall. The mound was located on the Hocking River, nine miles northward of Lancaster, Ohio (see _Tenth Ann. Rep. of Peabody Mus. of Arch. and Eth._, p. 51). The works at Hopetown, near Chillicothe, present several combinations of the square and circle. The two principal figures of these works are a square and circle—each containing exactly twenty acres. The discovery of these geometrical combinations—executed with such precision—in many parts of the country, lead to the belief that the Mound-builders were one people spread over a large territory, possessed of the same institutions, religion, and perhaps one government. These facts are highly important as shedding light upon the degree of their civilization. The evidence is ample that they were possessed of regular scales of measurement, of the means of determining angles and of computing the area to be enclosed by a square and circle, so that the space enclosed by these figures standing side by side might exactly correspond. In a word, their scientific and mathematical knowledge was of a very respectable order. [Illustration: Works in Liberty Township, Ross County, Ohio.] [Illustration: Celts. (Nat. Mus.) The large celt, upper line, from a mound (Tenn.). The others Surface Finds.] [Illustration: Aboriginal Chisels, Gouges and Adzes. (Nat. Mus.) Surface Finds.]