28 UNIVERSITY OF MISSOURI STUDIES 



eral to be deposited was the quartz. In some specimens there is 

 a very thin band of chalcedony, but this is not common. The 

 contact between the dolomite and the quartz is sharp. Most of 

 the dolomite grains present crystal faces to the quartz. There is 

 no difference in crystallinity between the crystals in contact with 

 the quartz and those at a distance from it. These so-called pipes 

 are really triangular columns of quartz and chalcedony, which 

 have the appearance of having been flattened or compressed. 

 They are in beds up to two feet and a half thick. They weather 

 out into large angular blocks. 



Where the quartz is in veins it shows essentially the same 

 features as in the cavities, chalcedony having been deposited first 

 and then the quartz. The quartz crystals grow out from opposite 

 sides and may or may not fill the vein. In all cases quartz is the 

 last mineral to be deposited and chalcedony the first. It was 

 probably the rate of deposition that determined which mineral 

 would be deposited, the slower growth producing quartz. 



There is a set of veins later than the chert and drusy quartz. 

 They are similar to the others save that, as a rule, they are with- 

 out chalcedony. They are of the same age as the quartz which 

 cements the rare chert breccias. 



The Potosi formation contains a number of cave deposits. 

 None of the caves were found with sufficient exposure to de- 

 termine their size or shape or the extent to which they were fill- 

 ed. The materials in them were angular grains of quartz, angu- 

 lar fragments of chert, and crystals of quartz with their faces 

 unscratched. These cave deposits do not appear to be very large, 

 but they are associated with the ore deposits. They were appa- 

 rently formed at a period when the region was above ground 

 water level, probably during the interval between the formation 

 of the Potosi and the Proctor dolomites. 



The Potosi formation is generally reported as being about 

 300 feet thick and such is probably its thickness in the eastern 

 part of this area, but north of Kingston towards Richwoods it is 

 apparently not more than 100 to 150 feet thick. Whether this 

 is due to faulting followed by erosion before the Proctor dolo- 

 mite was deposited could not be determined, as there were no 

 single beds which could be used as a datum plane to determine 



