MAIN MORAINIC SYSTEM OF THE MIAMI LOBE. 361 



canoe, there are sharp, gravelly knolls and ridges varying from 10 feet 

 up to 40 or 50 feet in height. 



From the Miami River northward this inner member has been described 

 as a portion of the eastern limb of the morainic system. 



THICKNESS OF THE DRIFT. 



In the eastern limb of this morainic system the thickness of the drift 

 has a known range from a mere trace up to 530 feet, with an average 

 of probably 200 feet. The thickness on the uplands is greater in Cham- 

 paign and Logan counties than farther south. The rock surface is much 

 more uneven than the drift surface, the eifect of the drift being to fill up 

 the valleys and lowlands to about the level of the preglacial ridges. 



The greatest amount of drift yet penetrated in Ohio is found in an 

 attempted gas-well boring at St. Paris, where, after penetrating to a depth 

 of 530 feet, the well was abandoned without reaching the rock. Within 

 3 miles south of this well, and at about the same altitude as its mouth, a 

 limestone quarry has been opened. The thickness of drift in the gas-well 

 borings at De Graff ranges from 33 to 300 feet, and at Bellefontaine frona 

 a thin coating up to 150 feet. 



Ill the Great Miami Valley there may be a continuous deep channel, 

 though it must be narrow, since the river in places has a rock bed, and rock 

 is near the surface throughout much of the valley bottom. The drift in 

 this valley has the following ascertained thickness: Near Piqua, 170 feet; 

 at Troy, 133 feet; at Dayton, 247 feet; at Miamisburg, 181 feet; and at 

 Hamilton, 210 feet There may be points in the valley where it is even 

 thicker than at Dayton. 



On the uplands, between the Great Miami and Sevenmile Creek, the 

 thickness is usually between 25 and 50 feet, but in the valley of Sevenmile 

 Creek a boring at Camden shows 180 feet, and borings near Eaton show 

 75 to 80 feet of drift. Between Sevenmile Creek and the State line the 

 thickness on the uplands ranges from 30 or 40 feet up to 100 feet or more. 

 In eastern Indiana the thickness ranges from 50 feet or less up to fully 250 

 feet, with an average thickness of 100 feet or more. 



What proportion of this drift was deposited previous to the formation 

 of the morainic system under discussion is difficult to estimate, there being, 

 so far as known, no widespread, well-defined soil or weathered zone separ- 

 ating the late Wisconsin drift from the early Wisconsin. Indeed, very few 



