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the course of the river lies over the blue limestone of the Cincin- 

 nati group until it debouches into the Great Miami at Dayton. At 

 Osborn it receives its last principal tributary, that of Mud run, the 

 southern boundary of which is formed by the Clinton limestone. 

 Haddix Hill, on which is an extensive system of earth-works con- 

 structed by the Mound-builders is one of the islands or "outliers" of 

 Clinton limestone left by some former erosive action ol great magni- 

 tude. Other detached masses of this limestone are found in the 

 neighborhood. The cause of this extensive erosion is usually ascribed 

 to glacial action of which there are abundant evidences. The pol- 

 ished and striated surfaces of the cap-rock of the Helderberg at 

 McComsey's quarry, east of Urbana, in Champaign county, of the 

 Niagara at the Springfield and Moore's quarries, of the Clinton lime- 

 stone at Snyder's Station in Clarke county, show that the great ice- 

 mass ground its slow way along over the edges of all the steps in the 

 series we have described. A very remarkable example of this glacial 

 polish has been brought to light in stripping the surface of Booher's 

 quarry at Taylorsville, in Montgomery county. This quarry is situ- 

 ated on the summit of a large island of Clinton and Niagara limestone, 

 which is bounded on the west by the valley of the Great Miami, and 

 is separated from the same formations on the east by an ancient eroded 

 channel which, in the opinion of President Orton, was the former bed 

 of this stream This channel is now occupied by Honey creek, flowing 

 north-west and emptying into the Miami, and by a small tributary 

 of Mad river which takes a southerly direction, reaching the river 

 at Osborn. In opening this quarry several feet of clayey soil were 

 removed to expose the rock which at this place is the lowest mem- 

 ber of the Niagara series, the Dayton limestone. The whole rocky 

 floor thus exposed, already several acres in extent, is smooth and pol- 

 ished and planed down almost to a perfect level. It is cut into 

 tables for flag stones and similar uses, blocks ten feet square being 

 sometimes removed which present so smooth and true a surface that 

 they seem to have been artificially dressed. The cyathophylloid cor- 

 als and other fossils which occur in the stone are finely exhibited in 

 vertical and cross sections. Comparatively but a small portion of this 

 polished floor has as yet been uncovered and its probable extent has 

 been estimated at not less than 200 acres. 



