GEOLOGY. 261 



OTHER MINERALS. 



" No minerals of much value, except those described in 

 the preceding sections, were detected in the district. 



" Chalcedony, agate, jasper, and cornelian, were found, but 

 not in great perfection. 



" On the southwest quarter of section seventeen, township 

 eighty-four, range five east of the fifth principal meridian, in 

 the Mineral Point and Blue River lead-mines, besides several 

 other localities, was found a white rock, which, by disinte- 

 gration, forms a white plastic material used in the manufac- 

 ture of porcelain : it is a hydrate of silica, containing a small 

 per centage of alumina, and is similar to that substance which 

 forms what are misnamed the ' chalk banks,' below Cape 

 Girardeau, Missouri. If obtained in sufficient quantities, it 

 would be of value in the manufacture of porcelain ; but I 

 failed to discover any extensive or continuous stratum of this 

 mineral. It has too large a per centage of silex, and too 

 little alumina, to rank as a true kaolin. 



*' No appreciable quantity of silver was discovered in any 

 of the ores of lead subjected to analysis ; neither was any 

 sulphuret of silver (as it occurs in the lead mines of the 

 Hartz) found in this district.* 



" In one or two specimens of galena, vestiges of arsenic 

 were detected. 



'* Little or no antimony is found in combination with the 

 lead ore of this district ; a circumstance which increases the 

 value of the ore, for lead ore contaminated with antimony is 

 of difficult reduction. 



" At McKnight's diggings, at Mineral Point, there occurs 

 along with the galena the ' black lead ore ' of the mineralo- 



* Ores of silver are rarely, if ever, found in this geological formation. 



