1134 A TREATISE ON METAMORPHISM. 



The very marked difference between deposits made by deep waters 

 and those made by shallow waters is beautifully illustrated by the Missouri 

 district. Thus in Joplin, where pumping has lowered the level of ground 

 water by 30 to 45 meters, the once clean openings, formerly below the 

 ground-water level, are now in the belt where waters are descending., The 

 caves which when first entered showed crystals fresh and untarnished are 

 now coated with oxide of iron and other products carried by the descend- 

 ing waters. Still more striking is the contrast between the clean mines in 

 which waters are ascending and the dirty ones in other areas in which 

 descending waters have produced an important effect to a considerable 

 depth. The latter mines are on smithsonite and calamine, and are muddy 

 and dirty to the last degree. Thick, sticky, iron-stained clay is everywhere, 

 adhering thickly to one's boots. The amazing contrast between the con- 

 ditions of the two classes of deposits is illustrated by the sulphide mines 

 of the Joplin -camp and the oxidized product mines of the Aurora camp 

 About 2 kilometers distant from Aurora is Sand Ridge, where the capping 

 Carboniferous impervious shale still remains. Here the descending waters 

 have not had a chance to enter, and the deep-seated waters are still rising, 

 and in this mine, which is only a short distance from the dirty oxidized 

 mines, are found the same clean sulphides and beautiful crystal-lined 

 cavities so characteristic of the mines of Joplin. 



In many cases, where currents are still rising, the ores are still being 

 deposited. This is believed to be true in the lead and zinc district of 

 southwestern Missouri, in the Comstock lode, and is known to be the 

 case at Steamboat Springs and Sulphur Bank. Where, in mines, streams 

 of clear water are found, with a uniform flow, unaffected by the seasons, 

 and deficient in oxygen, the evidence seems conclusive that the ore deposits 

 associated with such a circulation are the products of the deep circulation. 

 But in many districts the conditions of circulation which resulted in the first 

 concentration have ceased, the openings having been perhaps fully cemented 

 at the time of concentration, thus causing the circulation to die out. In 

 such cases the present circulation may be of an entirely different character, 

 even if the first main concentration was that of deep waters. 



A second criterion indicating that ores are deposited from the deep 

 circulation is the phenomenon of crustification, so strongly emphasized by 

 Posepnj^. (Fig. 28.) Posepny argues that the regular laminar arrangement 



