STEUCTUEE OF THE DEIFT BOEDER. 



Deep wells along Illinoian drift border in Muscatine County, Ioiva. 



49 



In northern Louisa County, near Letts, several wells have obtained 

 inflammable gas in sand below till at depths of 100 to 150 feet. These 

 wells are situated just within (south of) the ridge marking the limits of the 

 Illinoian drift, at a level perhaps 50 feet below its crest, or about 675 feet 

 above tide. It is reported by the residents that beds of black muck and 

 peaty material are found closely associated with this gas, and it is probable 

 that the gas is derived from the decomposition of organic matter in these 

 beds. The horizon seems rather low for the Yarmouth beds, unless the 

 Kansan till sheet has been eroded. Prof. F. M. Witter, of Muscatine, Iowa, 

 has presented a brief discussion of these wells in the American Geologist. 1 



The drift in the vicinity of Columbus Junction may exceed 300 feet 

 in depth. A well made by Dr. Daniel Overhalt in the Iowa River Vallev, 

 near Columbus Junction, at a level about 130 feet below the uplands, 



1 Am. Geologist, May, 1892, pp. 319-321. 



MON XXXVIII- 



