so 



LIMESTONES OF RED CEDAR, 



REGION OF DRIFT RES T I N C 0 N I. I M E S T OSES OF DEVONIAN I) A T E. 



SECTION III. 



TTS MINERAL CONTENTS. 



The structure and composition of the rocks which form the basis of this tract of 

 country are not unfavourable for the retention of minerals ; its physical features, 

 however, do not indicate a mineral tract. Along the course of our route, no symptoms 

 were observed of important axes of dislocation and disturbance. The surface is 

 comparatively level ; the ledges of rocks lie low and horizontal, without any abrupt 

 uplifts or sudden faults, as if be^yond the sphere of active action that has fissured, 

 and filled with metallic matter, the magnesian limestones lying to the northeast, 

 nearer to the Mississippi. 



SECTION IV. 



ITS RANGE, EXTENT, AND BEARINGS. 



The superficial area of the formation under consideration is much less than that 

 of any other system of sedimentary rocks of the District. It may be traced along 

 the course of the Mississippi River, for the distance of about thirty miles, viz. : from 

 near the head of Rock River Rapids, a few miles below Parkhurst, to the town of 

 Wyoming. Thence the formation ranges, with a northwesterly curve, up the valley 

 of Red Cedar River ; forming a belt, averaging, at first, some twelve or fifteen miles 

 only in width, but gradually enlarging, until, when in latitude 43°, it disappears 

 under the drift of Northern Iowa, it attains a width of from thirty to thirty-five 

 miles. 



Over a large portion of this tract of country, and especially on the high grounds. 



