Geology of Upper Illinois. 159 
from a greater depth. For it appears to be ascertained in respect 
to these ancient saline deposits, that the common salt in a state of 
perfect purity, forms the lowest stratum of the series, while the 
upper layers and members of the formation, such as marls and 
clays, abound in the sulphates, other more soluble chlorides, 
iodides and bromides.* 
-To what depth it may be necessary to penetrate in this region, 
in order to obtain a supply of salt water, may perhaps be inferred 
from the borings in Ohio, where they work down from seven to 
nine hundred feet, which is several hundred feet below the level 
of tide-water at the mouth of the Mississippi. Now, provided the 
salt-stratum lies at the same level in Illinois as in Ohio, (which 
perhaps is not an unreasonable conjecture, ) the borings we 
Illinois would not have to be carried as deep as in Ohio, - 
the surface in the latter region is obviously more elevated ion in 
the former. 
Iron Ores, Sand, Clay and Soil. 
Argillaceous carbonate of iron in balls, tuberose masses and 
kidney-shaped concretions, occur in the clay and marl beds of 
the Swanson ravine ; but whether in such quantity as will ulti- 
mately lead to extensive iron manufactures, cannot at present be 
determined, though when the coal comes to be extensively work- 
ed, enough ore will perhaps be obtained to furnish the region with 
a full supply of iron for castings. It is not uncommon to find 
balls of many pounds weight ; while strong indications of a con- 
tinuous stratum of the ore, several inches thick, exist at the coal 
opening on section thirteen. Its specific gravity is 3.025, and 
being mingled with limestone, its reduction will of course be 
effected with great facility. A sandstone moreover, is at hand 
for the construction of furnaces, while the coal will afford an ex- 
cellent fuel to be employed in the process. 
Tron-pyrites exists in the large coal stratum in two layers, each 
about an inch in thickness. As it is a variety strongly prone to 
decomposition, it can be employed to great advantage in in the 
ufacture of copperas, from which salt, both sulphuric acid and col- 
cothar, may be obtained, should their production be found an ob- 
ject in that region. 
* Report on Mineral and Thermal Waters, by Prof. Dauner, made to the Brit- 
ish Association for the Advancement of Science, in 1836, p 
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