122 



CARBONIFEROUS LIMESTONES 



white and rather gelatinous precipitate, having a slight tinge of green ; with caustic 

 potash, a copious white, gelatinous precipitate, partly soluble in excess ; the alkaline 

 solution, after filtration and saturation with hydrochloric acid, gives a precipitate 

 by supersaturation with ammonia. Hydrosulphuret of ammonia produces a copious 

 black and white precipitate, e^fr remaining distinct if the liquid be not shaken. 

 With carbonate of ammonia, a copious white precipitate ; with ferrocyanide of 

 potassium, a light blue precipitate ; with oxalate of ammonia, little or no precipi- 

 tate ; with chloride of barium, a copious white precipitate, insoluble in nitric acid ; 

 with nitrate of silver, a slight white precipitate, increasing by standing, and darken- 

 ing in the rays of the sun ; with chloride of platinum, a slight yellow precipitate. 

 These reactions with chemical reagents show that it is an acid solution of sulphate 

 of alumina, sulphate of potash, sulphate of protoxide of iron, and a little chloride 

 of potassium and sodium. It is, in fact, a double alum of potash and protoxide of 

 iron. The same kind of water was observed at several other localities on the 

 Upper Des Moines. 



About two miles above the Forks, on the left bank, two beds of coal are seen ; 

 the main one lies about twenty feet above the water-level ; the other bed, which is 

 only four to six inches thick, lies above, and is separated from the former by about 

 one foot of shale. Seams of a grayish clay run vertically and diagonally through 

 the principal coal-bed. 



About one mile higher, on the same side, a thin bed of coal is exposed, near the 

 water-level, associated with argillaceous and ferruginous shale, depositing in their 

 course a gelatinous, hydra ted oxide of iron. 



At several points between the last-mentioned localities and Hunt's Bend, desig- 

 nated on the chart of the river, a gray limestone occurs, a few feet above the 

 water-level. By exposure, this calcareous rock turns brown, no doubt from the 

 peroxidation of the iron. It is charged with Productus Flemingii ; Carclina nana 

 also occurs in it. Both above and below it are argillaceous shales, as seen on 

 Section No. 42, D. The upper shale includes nodules of ironstone, and septaria, 

 veined with red calcareous spar. Towards the summits of the ridges near by, under 

 the drift, there is a white limestone ; at a lower level, soft sandstone, like that at 

 the Forks, and still lower, a bed of coal. The relative thickness of this bed, and 

 the exact order of superposition, cannot be satisfactorily seen. Some of the darker 

 limestone will probably answer for making an hydraulic limestone. 



On Section 10, Township 80 north, Range 25 west, are alternations of red, 

 purple, and gray shales, as shown on Section No. 48, D. The red and purple shales 

 have somewhat the appearance of red pipe-stone, but are much softer, and subject 

 to disintegration ; they leave a pale red streak, approaching in character to the 

 soft red, argillaceous ochres, known to carpenters under the name of " keel." Three 

 to four miles higher up, is another bank of the same character. (See Section 49, D.) 



On Section 14, Township 81 north, Range 25 west, a gray productal limestone is 

 elevated thirty-five feet above the water-level, with a bed of shale and coal beneath 

 it, as seen on Section 44, D. In the shale, some crystallizations of selenite were 

 collected. The shale between that and the productal limestone includes septaria 

 and calcareous blocks that may afford hydraulic cement. 



