AND COAL-MEASURES OF IOWA. 119 



rocks have an undulating dip, so that the bed of coal and underlying clay are 

 brought to the surface, and as often again depressed beneath the water-level. 



On the southeast quarter of Section 8, Township 77 north, Range 21 west, a 

 brown, ferruginous sandstone lies fifty feet above the river. A portion of this rock 

 is a complete agglutination of vegetable remains, partly converted into hydrated 

 brown oxide of iron, and partly carbonized. A quarter to half a mile higher up, 

 ledges of sandstone, presenting cross-lines of deposition, and oblique ferruginous 

 veins, extend down to the water-level. Not far from Dam No. 26, and near the 

 line between Sections 10 and 11, Township 77 north, Range 22 west, there are 

 probably one or more beds of coal, but the sliding of the shales hides the greater 

 part of Section No. 38, D. Within three or four feet of the top of the shale, i. e., at 

 a height of forty to forty-five feet from the river, there is at this locality a band of 

 ironstone,* having a specific gravity of 3 '4 5, associated with some sulphuret of zinc, 

 the joints being coated with a crust of silicate of alumina. 



It appears from the above analysis that this ironstone is very analogous in its 

 composition to the ore known in Scotland as " Mushet's Black Band ;" the chief 

 difference being a smaller percentage of carbonaceous matter, and the substitution 

 of phosphorus for sulphur. 



It is more than probable that a repetition of the analysis of the " Scotch Black 

 Band" would give also a small percentage of phosphorus ; since I only succeeded in 

 detecting and estimating this element in the Des Moines ore, by methods which 

 have been introduced into analytical chemistry within the last few years. 



* An analysis of the ironstone by the humid method gave as follows 

 Bituminous or carbonaceous matter, 

 Insoluble earthy matter, .... 



Carbonate of the protoxide of iron, . 

 Carbonate of lime, ..... 



Carbonate of magnesia, .... 



Alumina, ...... 



Peroxide of iron, ..... 



Phosphate of iron, ..... 



After pounding and sifting the raw ore, a quantity weighing 

 was roasted, and exposed to a red heat in a shallow vessel ; 

 after roasting, it weighed .... 



Loss by roasting, 

 Being equal to 294 per cent. 



The colour, after roasting, was a purple-brown : an assay was then made in a black-lead crucible, at a 



high temperature, with the following ingredients, in the proportion of 



Grains. 



Roasted ore, ....... 865 



Bottle glass, . . . , . . . . 865 



Chalk, ........ 865 



Charcoal, ........ 134 



There resulted therefrom a button of light-gray iron, weighing 377 grains; equal to 43-5 per cent, of 

 the roasted ore, and 31 per cent, of the raw ore, differing only 2-5 per cent, from the percentage of 

 metallic iron by the humid method. 



01-0 

 07-6 

 65-0 

 07-2 

 10-0 



01- 8 

 04-8 



02- 6 



1000 

 1225 grains 



865 « 

 360 " 



