CHAPTER IV. 



CARBONIFEROUS SYSTEM.— (Concluded.) 



MIDDLE COAL-MEASURES. 

 1. GENERAL SURFACE FEATURES. 



The present chapter embodies the results of a rather 

 detailed reconnoisance of the counties occupied by the Middle 

 coal measures, made during the seasons of 1867 and 1869. 

 At the commencement of the work, the field was almost 

 wholly new, and we had barely the slightest knowledge of 

 this member of the coal-measure series. However, Prof. 

 Swallow, in his explorations in Missouri, had previously 

 recognized its existence in that State, and it was but reasona- 

 ble to expect to find the same formation within our own 

 limits. It is proper, and it gives me especial pleasure to 

 state that, during the progress of the field-work in this region, 

 I enjoyed every facility it was in the power of the Director of 

 the Geological Survey to afford me, and without which little 

 could have been accomplished in the short time necessarily 

 devoted to the work. As it is, we cannot presume to present 

 -the subject in a complete shape, since future explorations, 

 may, and doubtless will, add many important details, 

 although it is believed that, in the main, we have gained a 

 tolerably accurate knowledge of this member. 



Geographical JSxtent. Within the State of Iowa the Middle 

 coal formation occupies a narrow belt of territory in the 



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