474 GEOLOGY OF OHIO. 



This county lies south of the area of thickest Drift, which may be re- 

 garded as extending no further south than about the latitude of Sidney, the 

 county seat of Shelby county. Thence it begins to thin out southward. 

 The Miami River, where it enters the county in the north, cuts through 

 a perpendicular thickness of about seventy-five feet of drift-clay, gravel, 

 and bowlders, and all the water-courses which intersect the northern 

 portions of the county cut through the Drift to a depth of from thirty to 

 fifty feet. As might be expected, the material of the Drift varies greatly 

 in different localities. In some places it is composed of blocks whose 

 nature and condition show them not to have been transported far, and 

 commingled with them are gravel, sand, clay and quartz, and granite 

 bowlders in varying proportions. Some times the Drift is composed of 

 sand and gravel, with a small proportion of clay, or none at all, arranged 

 with more or less stratification. An illustration of this character of 

 Drift may be seen well developed on the new hydraulic works two miles 

 north ofPiqua, where they form a bed some forty feet in thickness, 

 cemented in great masses. The same formation is seen across the coun- 

 try, on the Stillwater, about one mile from the town of Clayton. The 

 Drift being largely composed of gravel and sand, there is no deficiency 

 of these valuable materials for all purposes. The streams wash out the 

 clay, and leave the gravel and sand, assorted in beds, along their entire 

 course. In other cases, the large accumulations, left by floods of former 

 days, afford convenient material for road-making in localities distant 

 from water-courses. Advantage has been taken of the abundance of 

 good material for road-making. The county is threaded in every direc- 

 tion with the finest of roads, most of which are entirely free of toll- 

 houses. 



Striated and smoothed rock-surfaces. — At Piqua, on both sides of the river, 

 where the quarries are exposed to view by the removal of the superin- 

 cumbent Drift, it is observed that the surface of the rock upon which the 

 Drift was lying, is worn smooth and polished, and variously striated and 

 grooved. At no point, I understood from quarry- men, does this character 

 fail to present itself. Lying upon the smoothed surface of the bedded 

 rock is a confused mass of yellow clay, with blocks of limestone, not 

 worn, of various sizes and in great confusion of position, together with 

 well-rounded gravel, both of limestone and granite, and other igneous 

 rocks, with larger bowlders of igneous rocks distributed throughout the 

 mass. All these have the appearance of having been arrested in the 

 midst of their course, in which they were grinding, marking, and pol- 

 ishing the surface of the bedded rock, as well as each other. There are 

 no indications of assortment according to specific gravity, or by any 



