1142, 143] MARLS OF THE ROTTEN LIMESTONE. 07 



HOUSTON MARL. 



Insoluble Matter (micaceous clay) 35.-750 



Potash 0.681 



Soda 0.197 



Lime 20.558 



Magnesia 1.366 



Brown Oxide of Manganese 0.305 . 



Peroxide of Iron 4.190 



Alumina 9.475 



Iron Pyrites 1.743 



Carbonic Acid 16.760' 



Organic Matter and Water 8.774 



99.799 



The iron pyrites contained in this marl (which is otherwise ad- 

 mirably adapted to light soils), renders necessary some caution in 

 its application. It should be allowed to lie exposed to the atmos- 

 phere as long as possible (several months at least), in order to effect 

 the decomposition of the minute crystals of pyrites, which results 

 in the formation of gypsum — enhancing the value of the material 

 as a fertilizer, in several respects. — Outcrops of the Houston marl 

 (which extends eastward to Kilgore's Ridge, and probably south- 

 ward to the Tibby) are scarce, but it is generally not far under- 

 ground in the district of its occurrence, as is known in each neigh- 

 borhood where wells have been dug. — A determination in the yel- 

 lowish-white, micaceous clay marl from Breuton's contract (near 

 Chawalla) on the M. & C. R. R., of the Carbonic Acid, considered 

 as belonging to carbonate of lime, yielded a result corresponding 

 to 21.0 per cent, of the latter substance, or to 11.8 per ct. ol puie 

 lime. 



142. As for the Rotten Limestone — itself, strictly speaking, a 

 marl, in most cases — it is unnecessary to mention its outcrops, since 

 no one who has his eyes open can fail to find them where they exist. 

 It is to be considered chiefly as a calcareous, stimulant manure ; 

 yet, as the analysis shows, it carries with it some nutritive ingredi- 

 ents, which account for its favorable effects even on the whitish, 

 highly calcareous bald prairie soil. In regard to the many import 

 ant uses which this calcareous material may subserve, the reader is 

 referred to what is said under the head of Lime and Marls, in the 

 General Part of the Agricultural Report. 



143. Marls of the Ripley Group. — Their distinguishing feature 

 is the visible grains of greensand, or glauconite, which they con- 

 tain, and to which they owe a higher percentage of potash, and 

 (with silica), in a more available condition, than seems to be the 

 case with the clay marls of the Rotten Limestone. This, and the 

 carbonate of lime contained in them, constitutes their chief value , 

 and since the former can be judged of by the eye, and the latter 

 Lv the strength of its effervescence ("boiling;") with strone; vinearar, 



R-7 * L 



