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 Odlitic 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 caleareous 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’) of the Upper Carboniferous Limestone of Lowa. 
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- 
ilica, i i ; ; ‘ 15:5 ; ‘ 053 
_ Carbonate of lime, : , ' 63-6 ; ; : 029-9 
Magnesia, . : ‘ , 12 , ; ‘ 7-4 
: Alumina, . : : ; 8-3 : ; ; 6-2 
 Protoxide of iron, ces : T-4 : : 1-8 
Eta M6 manganese, . i ; “4 ; . > trace 
Loss and bituminous matter, i... : ‘I 
