362 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



instances of buried soils have come to notice in this region. A comparison 

 of the thickness of the drift in the district lying outside (south) of the 

 moraines with that covered by them, leads to the conclusion that at least 

 one-half the drift was previously deposited. This constitutes probably the 

 most reliable method of making an estimate. It must, however, be con- 

 sidered a rude approximation, for it is probable that the ice sheet gathered 

 up and redeposited a portion of the drift that it overrode. 



STRUCTURE OF THE DRIFT. 



The portions of the moraine characterized by a gently ridged or a 

 swell-and-sag topography contain much more till than assorted material, 

 while the sharply ridged tracts and the prominent knolls, so far as opportu- 

 nity foi examination has been afforded, contain a preponderance of assorted 

 material. However, there are, on the gently undulating till tracts, numer- 

 ous places where gravel appears at the sui'face both in the knolls and the 

 intervening depressions, while wells indicate that beds of assorted material 

 are interstratified with or deposited in pockets within the till. In the 

 sharp gravellj^ ridges and knolls the presence of till is not uncommon 

 and it sometimes constitutes a considerable part of the material. While, 

 therefore, the structure admits of division into two classes, there appear 

 numerous abrupt changes in structure such as are characteristic of morainic 

 deposits. 



An interesting section of a sharp gravel knoll on an elevated portion of 

 the moraine may be seen IJ miles southwest of St. Paris. The knoll is 

 elongated in an east-northeast to west-southwest direction and was originally 

 very abrupt at its eastern end, rising within 10 to 15 rods to a height of 75 

 feet, while toward the west it had a gradual slope. The excavation began 

 in the eastern end and has been carried past the highest part of the knoll, 

 leaving only the western slope. The portion removed contained considerable 

 well assorted sand, gravel, and cobble, but the portion remaining presents 

 an interesting combination of beds, there being deposits of cobble, gravel, 

 and till, intergrading with each other, which are curiously disturbed and 

 contorted in their bedding. The gradual slope on the west side of the knoll 

 forbids tlie supposition that the beds owe their disturbance and contortions 

 to recent landslides, and leaves it probable that their form and position are 

 due to the molding and pressure exerted by the ice sheet. 



Sections of lowland gravel knolls may be seen in the vicinity of New 



