PAPERS OX GEOLOGY AND GEOGRAPHY 403 

 THE WELLS 



In general, the wells iu this area are drilled to a depth 

 of between 475 and 550 feet, depending on the elevation 

 of the curb of the well. The greatest difficulty in drilling 

 is encountered in going through the cherty Keokuk-Bur- 

 lington, and in some cases through the Moquoketa, which 

 breaks up easily but "will not mix with the water in the 

 hole and is therefore difficult to drill through. At the 

 present time wells are put down in from a week to 10 

 days, barring delays due to the failure of the drilling 

 machinery. The general procedure is to drill the wells 

 until the sand begins to show the first indications of 

 water. On the crest of the anticline this means a drilling 

 of about 50 feet into the Trenton before water is struck, 

 while in producing wells off the axis water is usually 

 encountered at about 30 feet. There are apparently 

 no formations which are consistent aquifers in any one 

 particular horizon. Parts of the Warsaw and Keokuk- 

 Burlington, however, are reported by drillers to be crev- 

 iced, and from such portions of these formations there 

 is the greatest influx of water into the hole above the 

 Maquoketa. 



THE SOLTRCE OF THE OH. 



In all probability the thick Trenton limestone and the 

 Maquoketa shale are the formations in this area from 

 which the oil has come. It is not an uncommon thing 

 to encounter a strong odor of oil or even a little black 

 oil in drilling through the Maquoketa shale. While this 

 fact in no way proves that the Maquoketa was one of the 

 sources of the oil in the Kimmswick it at least indicates 

 that the Maquoketa may well have furnished some of 

 the oil now found in the Kimmswick. 



The oil which has accumulated in the Waterloo anti- 

 cline probably migrated largely from the east and south- 

 east. The Valmeyer anticline shuts off migration from 

 the south and southwest, a syncline between the Water- 

 loo anticline and the Mississippi Eiver bluffs excludes 

 extensive migration from the west, and to the north other 

 smaller folds probably have acted as barriers prevent- 

 ing marked migration from that direction. 



