SURFACE GEOLOGY. 21 



further up the Ohio valley or in the beds of the tributary streams refer- 

 red to above. On the hills of the Coal Measures lying east of the Mus- 

 kingum (and Tuscarawas) and south of the glaciated and Drift area, no 

 bowlders or Drift deposits of any kind are found, and no Drift is discover- 

 able in any of the tributaries of the Ohio between the Pennsylvania line 

 and Marietta. The highlands in the angle between the Muskingum and 

 the Hocking are also free from Drift, and the same may be said of the 

 hills of the area inclosed by the valleys of the Hocking, Muskingum, 

 Scioto, and Ohio. West of the Scioto valley no Drift is found on the hills 

 bordering the Ohio, nor on the knobs which have been denominated the 

 Sun-Fish hills. The highest hills in Tuscarawas, Coshocton, Holmes, 

 Richland, and Knox come into the same category. 



All the highlands enumerated in the above list seem to have been 

 beyond the reach both of the glaciers and the floods of the Drift period, 

 and here we find the soil formed by the decomposition of the underlying 

 rocks. Over all other portions of the surface of Ohio the Drift deposits 

 were once spread in an unbroken sheet. 



The succession of these deposits and their most prominent character- 

 istics have been briefly noted in the earlier part of this chapter. They 

 will now be described somewhat more in detail, in order that the features 

 they present may be better' understood, and that the history read from 

 them may be intelligently judged. 



ERIE CLAY. 



Over most of the glacial area in Ohio we find resting directly on the 

 planed and polished rock surfaces a sheet of variable thickness of blue or 

 gray clay. As it generally appears, this clay is unstratified, and is thickly 

 set with small pebbles or fragments of stone, and it also contains a few, 

 usually small, bowlders." Hence it may, with propriety, be denominated 

 a bowlder clay, and it closely corresponds in position and character with 

 the clay bed called by that name which covers so much of the glaciated 

 surface in other states and countries. Though generally exhibiting the 

 features that I have assigned to it, the clay bed under consideration does 

 not always present these characters, as it is sometimes rudely stratified 

 throughout, and in many localities the upper portion is very finely and 

 distinctly laminated and without pebbles. These phases of the deposit 

 shade into each other, however, in such a way that it cannot well be 

 separated into distinct formations or strata. I have, therefore, consid- 

 ered it as one formation, and have distinguished its divisions simply as 

 the bowlder or lower and the laminated or upper member, and have called 

 the whole the " Erie clay," accepting the name conferred by Sir William 



