112 



CARBONIFEROUS LIMESTONES 



All along the eastern margin of the Illinois and Indiana coal-field, as well as the 

 western margin of that portion of the same basin, which stretches through Ohio, 

 Kentucky, and Tennessee, where productive salt-works have been established, the 

 base of the coal formation, down to the Archimedes, Pentremital, and Oolitic lime- 

 stones, is arenaceous, and the borings for salt water at these localities have uniformly 

 been carried through porous and cellular sandstones with vegetable impressions. 

 The lower members of the Iowa coal-field, as has been already stated, consist chiefly 

 of calcareous rocks, especially around the southern and western margin of this basin 

 on the Des Moines and Missouri Rivers. In this respect the Iowa coal-measures 

 differ essentially from those of Ohio, Virginia, Kentucky, and Indiana. 



This fact serves to clear up a difficulty which has hitherto existed with regard 

 to the true geological position of certain limestones in the vicinity of St. Louis, 

 which are now shown to form that portion of the Carboniferous Limestone Series, 

 which is known in Yorkshire as the Upper or Yoredale Series, and is one of the last 

 members (d f ) of the Upper Carboniferous Limestone of Iowa. 



At several localities in the neighbourhood of the brine springs above mentioned, 

 at an elevation of ten or twelve feet above the springs, is a bed of limestone, having 

 hydraulic properties, and an argillo-calcareous rock, presenting that peculiar con- 

 centric, crimped, conical structure, known in Germany by the name of Tutenmergel, 

 and usually attributed to a shrinkage of the strata. It may, however, in my judg- 

 ment, be more correctly referred to an imperfect crystallization, produced by a 

 process of infiltration through beds of marly, argillaceous matter ; since I found the 

 structure displayed in greatest perfection higher up on the Des Moines, in a band of 

 three or four inches of calcareous spar, possessing an arragonite structure, included 

 in marly shales ; the concentric conical surface having only a thin superficial coating 

 of earthy matter, apparently carried down mechanically during the passage of the 

 calcareous matter through the argillaceous matrix. 



In connexion with these beds are thin seams and isolated crystals of selenite, 

 the whole being covered by argillaceous slaty clays. Sandstone is found in the 

 higher grounds, but its junction with the inferior beds cannot be satisfactorily seen 

 at this locality. 



The dark, bluish gray, earthy variety of hydraulic limestone* contains 63*5 per 



* Analyses of two varieties of hydraulic limestones, from the Saline Branch of Soap Creek, gave the 



following results. 



Dark Earthy. Light Gray. 



Water of absorption, . . 001-5 . .001- 



Silica, . . . 15 5 . . . 053- 



Carbonate of lime, . . . 63-6 . . 029-9 



Magnesia, . . . . 12 . . 7-4 



Alumina, .... 8-3 ... 62 



Protoxide of iron, . . . 7*4 . . . 1-8 



" manganese, ... -4 trace 



Soda, ..... -4 -6 



Potash, ..... -3 trace 



Loss and bituminous matter, 1 -4 . -1 



1000 1000 



