SCHMIDT LEAD AND ZINC DEPOSITS OF S.W. MISSOURI. 25 I 



entire disintegration of these chert beds, which took place locally, 

 produced the irregular deposits in loose chert, and finally local 

 infiltrations of quartz into the broken rock-masses, under con- 

 tinued deposition of ores, created the fifth kind of deposits afore 

 described, which consequently must be considered as the latest. 

 The various processes by which all this has been effected must 

 have taken an enormous amount of time for their completion. 

 The dolomizationof limestone is naturally a very slow process; 

 so is also the dissolution of limestone, even then when we assume 

 that the waters circulating in the rocks were formerly much more 

 acidic than they are now. Very slow is also the deposition of 

 quartz, because water is capable of dissolving but very little of it. 

 That the deposition of the ores must have been very slow, ami 

 must have ensued from exceedingly thin solutions, is shown by 

 the large size of the crystals. In many places the crystals of ga- 

 lena reach a diameter of three inches and more. The subcarbo- 

 niferous rocks in which these processes have taken place are very 

 old. Their age must be estimated, according to some remarks of 

 Professor Dana in one of his recent publications, at twenty mil- 

 lions of years at the very least. Thus we see that these processes 

 had ample time to take place, even under the supposition that the 

 solutions which effected them were but little, if any, more satu- 

 rated with acids or with metallic oxides than many of our present 

 spring waters. 



From all what I have said on the character of the lead deposits 

 of Southwest Missouri, it appears that these deposits do not fill 

 large vertical fissures, cutting through thickly stratified or through 

 unstraliiied rocks : they have in no place the slightest resemblance 

 to true veins. But they are spread through the rocks horizontal- 

 ly, and extend, in varying richness, over the whole southwestern 

 part of the State. The layers of rocks in which the ores are found 

 at present lie only from 40 to 120 feet below the surface of the 

 ground, and are therefore much easier to reach and much cheaper 

 to mine than similar ores which occur in some other countries in 

 the form of veins. If we compare the work and the production 

 of a poor Saxon miner, who. at a depth of two to three thousand 

 feet, drills and blasts on a vein often but one or two feet wide, and 

 mostly composed of much hard gangue and but little ore: — if we 

 compare this with the work and the production of a Missouri 



