124 Trans. Acad. Sci. of St. Louis. 



variety, is occasionally intermixed, and less frequently pyrite. 

 The lignite is brown in color, shows an eminent wood structure, 

 and dries out on prolonged exposure, becoming heavily 

 checked and very tender. 



The coarse sand and gravel of recent age that overlays the 

 sandstone is cross-bedded (showing that it is a channel deposit 

 of the river), and contains abundant fragments of drift-wood 

 that is more or less lignitic. None of these lignitic fragments 

 in the sand contain any blende, which shows that the zinc was 

 introduced before they were deposited. 



This occurrence of blende in this basal coal-measure sand- 

 stone is very interesting from its bearing on the problem of 

 the origin of our Missouri zinc deposits. For though only 

 found in specimen quantities, it shows that during or since the 

 coal-measure epoch, this coarse-grained, porous sandstone has 

 been permeated with solutions carrying zinc-sulphate, from 

 which by the reducing action of the lignite, the soluble zinc- 

 sulphate has been reduced to the insoluble zinc-sulphide or 

 blende, and precipitated in the interstices and cracks of the 

 shrinking lignite. The blende is only found in the lignite, so 

 that large amounts of zinc may have been present in the sand- 

 stone, but was only retained where locally converted by the 

 lignite into the insoluble blende. 



The nearest known occurrence of zinc is in the quarries in 

 the underlying St. Louis limestone that are worked five to ten 

 miles south, where small disseminated grains of crystalline 

 blende occur occasionally in the geode-bearing magnesian 

 limestone beds ; the latter are sufficiently porous for the 

 feeble infiltration of solutions, and organic matter in the 

 limestone seems to have precipitated slight amounts of zinc. 

 Numerous other instances of occasional disseminated grains 

 or nodules of zinc have been observed in the neighboring 

 limestones, and unsuccessful attempts at zinc-mining have 

 been made near Troy, in Lincoln County. 45 miles northwest, 

 and at Hannibal, 90 miles, at the base of the Sub-Carbonif- 

 erous. The nearest producing zinc mines are 50 miles south, 

 at the Valle Diggings, in St. Francois County, where the zinc 

 occurs in gash-veins, associated with galena in magnesian- 

 limestone of Lower Silurian or Cambrian age; while the great 



