CHAPTER I. 



AZOIC, LOWER SILURIAN, UPPER SILURIAN, AND 

 DEVONIAN SYSTEMS. 



Although the labors of the Geological Survey, since its 

 present organization, have been principally confined to the 

 western half of the State, a general examination has also 

 been made of the formations of the eastern half. Therefore, 

 a general review of all the formations in the State will be 

 given in this and following chapters; but more especial 

 attention will be paid to those which belong to or overlie the 

 Carboniferous system. 



The stratified rocks of Iowa range from the Azoic to the 

 Mesozoic inclusive, but the greater portion of the surface of the 

 State is occupied by those of Palaeozoic age. The accompa- 

 nying section of the rocks of Iowa, show each of these 

 formations in their order, together with the method of their 

 classification adopted in this report. 



1. AZOIC SYSTEM. 



HUK0NIA^(?) GROUP. 



THE SIOUX QUARTZITE. 



Area and General Characters. This formation is found 

 exposed in natural ledges only upon a few acres in the 

 extreme northwest corner of the State. Its area being so 

 small in Iowa, it could not be conveniently represented on 



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