Ancient Ruins.-—-The Chicago American contains! a diagram of a supposed an-.cient city, the ruins of which have lately? been discovered in Wisconsin. The individual who prepared it gava.at the same timo (the following.history..;. .“Having some business to do in the office of Mr. Kilbourne, one of the principal proprietors of West Milwaukee,, one of the gentlemen engaged in the office took out a diagram of the ruins, and asked the visitor* present if they had ever 1 leard of the wonderful discovery that had lately been made on Rock river? At the same time remarking, that he had obtained an, exact delineation of the whole work, which consisted of -an inner wall of rectangular shape, -being about twelve feet thick at the base, and although crumbled .down, still left about 5 feet high all round. Without this wall, which may be called the citadel of the ancient city, the ruins of another, both made of well feirntbricky was discovered, but not represented in the above sketch,, which appeared to be aboutthree miles square. A specimen of the brick was exhibited to the visiters, which was taken from the miier wall, the character ,of which cc uld not be mistaken, being a true fracture from a icell burned . brick. This Specimen is now in the possession of Mr. Kilbourh, at Milwaukee, who informed the visitors that it certainly was ' taken from the ruins, and had no doubt of their existence ;but whether in the form and to the extent represented, he had no personal knowledge to confirm. He said it was his intention, however, to visit the spot to satisfy himself on the first .convenient leisure, and added: “if trpe, it is not only one of the most remarkable discovery of ruins, and other vestiges of a race of people, now extinct, that once inhabited this portion-! of America, but may lead to a new train of research and investigationupon this hitherto difficult and mystifying subject.”