CARB0NIFEK0US SYSTEM. 257 



exactly coincident with the slope of the streams. There may 

 be northerly and southerly folds passing through this space 

 beneath the heavy deposit of drift, but they are very slight if 

 they exist at all. 



Thus we have the phenomena of a very considerable west- 

 erly dip of the Sub-carboniferous rocks of southeastern Iowa, 

 which dip has been gradually lessened by the greater 

 elevation of all the formations together in the central portions 

 of the State than they have at its borders, until we find a 

 part of the upper super-imposed formations having almost 

 no westerly dip at all, in the region of its greatest elevation. 



The coincidence of the southerly dip of the strata with 

 the slope of the stream is distinctly shown in the valley 

 of the Nodaway river. Here the thin bed of coal, before 

 referred to as the only one yet known to exist in the Upper 

 coal-measure formation, forms an easily recognized horizon, 

 and may be readily traced by its exposures at frequent 

 intervals from a, point three miles above Quincy, in Adams 

 county, to the southern boundary of the State, a distance 

 of forty miles. In all this distance wherever the bed of coal 

 has been found, it occupies about the same elevation, 

 amounting to only a few feet above the water of the stream. 

 This coal and its associated beds are referred to about the 

 horizon of Nos. 6 to 10 inclusive, of the Winterset section. 



Passing now to the northwest corner of Fremont county we 



identify, without hesitation, the same bed of coal there, 



together with its associated strata in the bluffs of the 



Missouri river. This point is fifty -four miles from the one 



first named in Adams county, and forty -five miles from the 



one in the valley of Nodaway river near the State boundary. 



By drawing lines on the map connecting these three points, we 



enclose a large triangular space, which may be taken to 



indicate the position of an imaginary triangular plane 



formed by the strata of this part of the State, having its sides 



respectively forty -five, fifty -four, and forty miles in length, 



Although the assumed boundaries of this plane are imagin- 



nary, we know that the position of the strata in such a plain 

 33 



