238 GENEEAL GEOLOGY. 



ago it was used for the manufacture of hydraulic lime. The 

 lime thus produced was used in some of the now abandoned 

 works of the "Des Moines River Improvement," but it seems 

 to have been at least only a partial success. 



On the whole then, it will be seen that the portion of the 

 State which is occupied by the Lower coal-measures is not 

 well supplied with building stone. Its brick clays are, 

 however, abundant and good, and fuel for burning bricks 

 is cheap and accessible. The clays used for bricks are the 

 drift clays which have been derived mainly from the shales 

 and clays of the coal-measure strata ; while that used for 

 pottery is taken from the beds which almost invariably 

 underlie each bed of coal. The clay of some of these beds 

 is purer and better than that of others, and excellent 

 common stoneware is manufactured from it. Some of the 

 clays or clayey shales of the Lower coal-measures contain 

 so much oxyd of iron, giving it a brownish red color, that 

 with proper grinding, it would furnish a fair article of 

 common mineral paint, similar to that now known in the 

 market under the name " pecora." 



In another part of this report, it will be shown that some 

 springs containing a little salt are found issuing from the 

 Lower coal-measure strata ; and an explanation of the 

 origin of the term "Saline lands of Iowa" will also be 

 found there. 



In other countries, and in other parts of our own country, 

 much valuable iron ore is found among the strata of the 

 coal-measures, but although this ore in the form of hematite 

 is almost everywhere present among similar strata in Iowa 

 in small quantities, it is seldom of sufficient purity, and has 

 never been found in sufficient amount to be profitably worked, 

 even if suitable fuel for smelting were abundant and cheap. 



Among other minerals found among the strata of the 

 Lower coal-measures are sulphates of lime, strontia, and 

 baryta, and the sulphurets of zinc and iron. All except the 

 latter are found in very small quantities and very rarely ; and 

 they are all of no practical value, .their presence there being 

 interesting only as mineralogical facts. 



