Geology of Upper Illinois. 159 



from a greater depth. For it appears to be ascertained in respect 

 to these ancient sahne 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 doAvn 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 in Upper 

 Illinois would not have to be carried as deep as in Ohio, since 

 the surface in the latter region is obviously more elevated than in 

 the former. 



h'on 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. 



Iron-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 the man- 

 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. Daubeny, made to the Brit- 

 ish Association for the Advancement of Science, in 1836, p. 18. 



