SURFACE GEOLOGY. 25 



stantly present, but it is less conspicuous than farther north, because it 

 is thinner, is more generally covered with later deposits, and has been 

 cut away along the great channels of drainage, through which the waters 

 of the lake-basin were drained into the Ohio. It is a somewhat singular 

 circumstance that the bowlder clay is more continuous in the counties 

 which lie along the margin of the Drift area, than nearer the divide 

 where the Drift deposits are thicker; probably for the reason that shore 

 waves and draining streams have been more general and powerful in 

 their action, and have removed the clay in the region where it is less 

 abundant. Throughout most of the southern counties of the State the 

 bowlder clay may be found in many exposures, forming the basal portion 

 and perhaps half the thickness of the upland drift. In the valleys it is 

 less constantly present. In the reports of Prof. Orton, on Hamilton, 

 Clermont, Highland, Montgomery, and other counties, more detailed 

 descriptions of the Drift deposits of southern Ohio will be found than 

 can be given here. A type section, however, from Clermont county, 

 quoted from Prof. Orton's report, will serve to give a good general idea 

 of the relations of the bowlder clay to the other members of the Drift 

 series. 



SECTION OF DRIFT, SOUTHERN OHIO. 



No. 1. Soil. 



No. 2. Surface clays, generally white ; sometimes blackened by swampy 



conditions, entirely free from gravel 1 to 8 feet. 



No. 3. Yellow clays, abounding with gravel, with occasional bowlders, 



often constituting the surface instead of No. 2 ; seldom over... 10 feet. 



No. 4. Forest soil ; a stratum of carbonaceous clay, containing vegetable 

 matter, with occasional beds of peat; in some districts re- 

 placed by bog iron ore 1 to 8 feet. 



No. 5. Blue bowlder clay, or hard-pan, with occasional layers of sand 



intercalated, resting on the rocky floor 5 to 20 feet. 



Prof. Orton thus describes the bowlder clay of this region: "The 

 bowlder clay, or hard-pan, is found very generally, but not universally, in 

 the northern and central regions of Clermont county. It is shown in 

 many of the natural sections that are furnished by the streams, and in 

 such artificial sections as are carried to sufficient depth. It is covered by 

 varying thicknesses of the remaining members of the series. Where 

 the total depth of the Drift beds reaches twenty feet, a full half of the 

 section generally belongs to the bowlder clay. It cannot be confounded 

 with any other formation in the district in which it occurs. It is 

 composed of dark-blue, fine- grained, and tenacious clay, holding pol- 

 ished and striated pebbles and bowlders. Most of the pebbles are de- 

 rived from the blue limestone formation, though frequent representatives 



