AND COAL-MEASURES OF IOWA. 



121 



One atom of carbonic acid, 

 One atom of protoxide of iron. 



The analysis given by Dr. Thomson in his " System of Chemistry and Mine- 

 ralogy," vol. i. p. 446, of the light grayish black variety of " Scotch cross-basket 

 ore," as determined by Dr. Colquhoun, is still more closely allied to these Des Moines 

 ores ; both containing very nearly the same amount of carbonic acid, and protoxide 

 of iron, and differing only in the Iowa ore, containing three per cent, more of per- 

 oxide of iron, one per cent, less carbonaceous matter, and two per cent, less of 

 earthy matter ; consequently it has a rather higher specific gravity than the Scotch 

 ore. 



The composition of the " Cairnhill Black Band," analyzed by Dr. Colquhoun, 

 gives within a fraction of one per cent, the same amount of protoxide of iron, but 

 less carbonate of lime and magnesia, and more carbonaceous and earthy matter. 

 This is the measure connected with the Ell-coal, and was the first of this species of 

 ore discovered and wrought. The percentage indicated by Dr. Colquhoun as the 

 average yield of the " Cairnhill Black Band," corresponds exactly with the percentage 

 of iron (33 per cent.), obtained from my analysis, in the humid way, of the Des 

 Moines ore. The large amount of carbonaceous matter in the Cairnhill ore (17 per 

 cent.), indicates that the Iowa ore would require a larger amount of carbon for its 

 reduction than the Scotch ore. If the former ever should be wrought for iron, as 

 it doubtless will, when the country becomes more densely populated, it will be 

 interesting to see whether the iron produced on the large scale has cold-short pro- 

 perties, in accordance with the views advanced by Mr. Rinman at the meeting of 

 the British Association at Birmingham. 



Coal has been found at various places in the vicinity of Dudley, as well as on 

 Middle River and its branches. The carboniferous rocks above Dudley are covered, 

 however, by a considerable thickness of marly earth, perhaps of the age of the 

 Loess of Germany, resting on ferruginous conglomerate, a section of which, eighty 

 feet high, presents itself on the Des Moines, on Section 23 (?), Township 78 north, 

 Range 23 west. 



On Section 15, same township and range, a bed of coal lies twelve to fifteen feet 

 above the water, enclosed between beds of shale, the whole overlaid and partly con- 

 cealed by the drift. A bed of corresponding thickness is also seen on the right bank 

 of the Des Moines, half a mile below the Forks, on Section 11 (?), Township 78 

 north, Range 24 west. 



Carboniferous Rocks of the Des Moines, above the Raccoon Fork. — On Section 4, 

 Township 78 north, Range 24 west, is a seam of coal, known as Hall's Coal-bank. 

 It is between two and three feet in thickness, over and underlaid by argillaceous 

 shale, the whole being covered by soft sandstone, schistose below, and thicker- 

 bedded above. (See Section No. 40, D.) The upper part of the coal is impregnated 

 with iron pyrites ; the lower part is of better quality. 



From the argillaceous layers there oozes a mineral water, having a faint brown 

 tinge, acid reaction, and strong styptic taste. This water gives with ammonia a 



16 



