APPE^TDIX. 353 



Fluate of Lime. 



Fluor-Spar. — On the United States Mineral Eeserve, Pope 

 County, Illinois. This locality is abundant, and the mineral 

 readily and constantly to be obtained. I first obtained specimens 

 in June, 1818, and afterwards visited it in July, 1821. It is dis- 

 seminated in loose masses throughout the soil, and in veins in the 

 calcareous rocks. The spot most noted and resorted to, and 

 where the original discovery was made, is four miles west of Bar- 

 ker's Ferry, at Cave-in-Eock, on the banks of the Ohio, and about 

 twenty-six miles, by the course of the river, below Shawneetown. 

 It is situated in the midst of a hilly, broken region, called the 

 Knobs, a tract of highlands intervening between the banks of the 

 Ohio and the Saline. The distance of this range from north to 

 south, or parallel with the course of the Ohio, cannot be stated. 

 It probably extends from near the banks of the Wabash River 

 to the Little Chain of Rocks. Its breadth — from Barker's Ferry, 

 west, to Ensminger's, at the Saline, is about twenty miles. It 

 thus separates, by a rocky border, the prairies of the Illinois from 

 the current of the Ohio River. These knobs, wherever observed, 

 bear the indubitable marks of secondary formation, and may be 

 stated to consist, essentially, of compact limestone resting on sand- 

 stone. The sandstone is sometimes so much colored by iron, and 

 by globular or irregular masses of iron stone, as to give that rock 

 a very singular aspect. This may be particularly instanced in 

 the mural front of the Battery rocks on the banks of the Ohio. 

 Every part of this formation has more or less the appearance of 

 a mineral country ; and it is already known as the locality of 

 ores of lead, iron, and zinc, of crystallized quartz, of opal, heavy 

 spar, crystallized pyrites, and of very perfect fossil madrepores. 

 In one place (near the head of Hurricane Island) this spar forms 

 a very large and compact vein, dipping under the bed of the 

 Ohio. AVhere the rock has been explored, it is found in connec- 

 tion with sulphuret of lead, but it has been mostly procured, be- 

 cause most easy of access, in the alluvial soil. I went out about 

 half a mile west of the Ohio, where a new locality has been opened, 

 and, in removing about five or six solid feet of earth, procured as 

 many specimens as filled a box of fourteen inches square. None 

 of these were more than two feet below the surface. One of these 

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