32 GEOLOGICAL STRUCTURE OF THE 



and at all events marks the termination of the se- 

 condary soil. 



The fluate of lime, so abundant and beautiful in 

 the secondary calcareous rock of Derbyshire, in 

 England, is not altogether wanting in the valley of 

 the Mississippi. In 1810, Mr. J. Bradbury favoured 

 me with very fine specimens of white, blue, and am- 

 ber colored fluor, from a lead mine, at the Rock 

 and Cave, in the vicinity of the Ohio. Another lo- 

 cality of this mineral was pointed out to me, also in 

 1818, as existing near Centreville, in the county of 

 Logan, in Kentucky. In the same locality with 

 that described by Mr. Bradbury, Mr. Jessup found 

 it in abundance on the surface for a space of thirty 

 miles, accompanied by a vein of galena. In its 

 vicinity, Mr. J. also met with nodules of argillaceous 

 iron ore, containing blende. But fluor has never 

 yet been found on the banks of Missouri, as assert- 

 ed by Mr. Claiborne. 



The floetz trap formation, or that variety of it. 

 termed in Derbyshire, toad stone, and which there 

 so signally detanges the strata and metalliferous de- 

 posits, in no form makes its appearance throughout 

 this secondary platform, the only anomalous bed in 

 any manner analogous to this, is the greenish, and 

 apparently ferruginous arenilitic rock, with a sparry 

 calcareous cement, and bordering on graawacke, 

 which appears beneath the newer floetz lime- stone of 

 Red River. 



