IOWA ACADEMY OF SCIENCES. 59 



COAL MEASURES OF POWESHIEK COUNTY. 



BY ARTHUU J. JONES. 



Nearly all of Poweshiek county is covered by loess and drift to such a depth 

 that little is known concerning the underlying stratified formations. Almost the only 

 natural exposures of rock in the county are in the southwestern part where there 

 are frequent outcroppings of Saint Louis limestone and Coal Measure strata; for 

 the remainder of the county the only data obtainable are from wells sunk in various 

 places. From these it appears that the northern, middle and eastern portions of the 

 county are underlaid immediately below the drift with Lower Carboniferous strata. 

 The Saint Louis limestone was found at Grinnell a little over 200 feet from the sur- 

 face, while a little farther east the drift is still thicker with no indication of shale 

 or coal. Coal has been found in paying quantities a few miles west of the county 

 line in Jasper county at the Black Oak mine, and also a short distance from the 

 south county line at the Evans mine. A direct line drawn from one of these mines 

 to the other would cut across a considerable part of the southwestern corner of 

 Poweshiek county. At Thornburg also, not far from the southeast boundary, coal 

 mines are being operated. But although coal has been found on both sides so 

 near, few workable veins have yet been found within the county limits. 



At Searsboro two drill holes were sunk during the past summer and small 

 quantities of coal were found not over ninety feet from the surface. Almost 

 directly south of this place near Moore there are numerous traces of coal. Here 

 the Saint Louis limestone appears for several miles along the north Skunk river. In 

 the hills south of the river where they have been undisturbed, the Coal Measures 

 are seen to lie unconformably upon the limestone. In a number of places in these 

 hills prospect holes have been sunk but only a small amount of coal has ever been 

 taken out. A short distance southeast of Moore, on the south side of the river, 

 there is a fine exposure of limestone and shale. Here there is a blutf which shows 

 over forty feet of Coal Measure strata with the Saint Louis limestone appearing at 

 the base. At this place there are seen two seams of coal, the lower eighteen inches 

 thick and the upper twelve. They are separated by twenty feet of shale and a 

 thin layer of impure limestone which is only a few inches below the upper vein. 

 Here a drift was at one time operated, and in a ravine near by considerable quan- 

 tities of coal were taken out and sold to local trade. 



