GEOLOGY OF SOUTHWESTEKN IOWA. 367 



and many of those adjoining, are furnished with lime from 

 these quarries, and also with a large part of their stone for 

 common uses. 



The clay before mentioned as occurring at the base of the 

 sandstone exposure at Mr. Johnson's, a few miles above Red 

 Oak, is very plastic, and is reported to have been used for 

 common stone-pottery with good success. The red clayey 

 bed before mentioned as occurring near Frankford, is so ferru- 

 ginous that it may be very properly called clayey ochre. Mr. 

 J. B. Packard, of Red Oak, has erected a small mill for 

 grinding it into material for paint. When finely ground and 

 mixed with linseed oil, it makes a serviceable paint without 

 any other admixture where the color is not objectionable. It 

 may of course be mixed with white lead, and the color thus 

 modified. In chemical composition it somewhat resembles 

 the paint known in the market as pecora. 



14. MILLS COUNTY. 



Boundaries and Area. Mills county lies immediately 

 north of Fremont, west of Montgomery, and south of Potta- 

 wattamie counties, and is bounded on the west by the 

 Missouri river. It is eighteen miles across from its northern 

 to its southern boundary, and about twenty -four miles 

 in its widest part from east to west. In consequence of 

 the meandering course of the great river, it contains some 

 small fractions above twelve regular congressional townships, 

 and is consequently estimated to contain about two hundred 

 and eighty-eight thousand acres. 



Drainage and Surface Characters. The principal streams 

 of Mills county are the West Nishnabotany, its tributary 

 Silver creek, and Keg creek. The whole surface being 

 occupied by the Bluff Deposit, their valleys have the peculiar 

 characteristics which it everywhere imparts to those of the 

 tributary rivers, somewhat resembling the valleys of the drift. 

 That of the West Mshnabotany is of the same general aspect 

 which it and its associate, that of the East Nishnabotany, 



