428 Allen, Crenshaw, and Merwin — 



from the water and which has been shown by analysis to consist 

 largely of ferrous sulphide mixed with much smaller quantities 

 of the sulphides of zinc, lead and copper. Cementing together 

 the sand grains of both springs was also found pyrite in 

 microscopic crystals, on many of which Merwin was able to 

 identify the cube and octahedron. JVb marcasite was found. 

 The waters of these springs closely resemble that of deep wells 

 in the same geological horizon ; they are predominantly alkali 

 chloride and carbonate waters, they smell of hydrogen sulphide 

 and are faintly alkaline.* Thus it becomes evident that the 

 alkaline nature of the water irrespective of the temperature is 

 sufficient to condition the formation of pyrite. Mr. Siebenthal 

 has kindly placed at our disposal two samples of sediment from 

 deep wells which further correlate natural processes with those 

 of the laboratory. One of these wells is in St. Louis, Missouri, 

 the other in Columbus, Kansas. The waters from both wells 

 are of the same general character as the springs ; they are not 

 only decidedly alkaline, but contain a recognizable excess of 

 soluble sulphide. The mud was deposited or settled after the 

 waters had been pumped into storage reservoirs and had stood 

 for an unknown time, probably about a year.f The sludge 

 consisted of ferrous sulphide, free sulphur, which was dissolved 

 out by carbon disulphide, and a substance having the color of 

 ground pyrite, insoluble in hydrochloric acid, giving tests for 

 both iron and sulphur, and showing no crystal form when 

 examined under the microscope. In addition to these products 

 the sediment from the Kansas well contained also a crystalline 

 substance resembling pyrite but in crystals too small for 

 identification.;); Now, we know that a soluble polysulphide 

 gives with a ferrous salt a precipitate of ferrous sulphide and 

 sulphur, and we have observed in the laboratory that they unite 

 at 100° to form amorphous disulphide, which in time crystal- 

 lizes to pyrite. In the waters of the springs and wells which 

 we have just cited, it is plain that the same processes go on 

 very slowly at ordinary temperature. 



B. Paragenesis of marcasite andwurlzite with calcite. — We 

 have stated previously that marcasite is commonly a product 

 of surface waters and have concluded that it may have formed 

 from acid solutions, because the solutions from which it 

 crystallizes are doubtless formed in many cases by the oxidation 



*Both are alkaline toward rosolic acid and the White Sulphur water gives 

 a trace of color with phenolphthalein. Small recent calcite crystals and 

 recent quartz crystals occur in the Black Sulphur Spring. 



f Mr. Siebenthal's investigations have brought out the fact that these are 

 not unusual cases, but that the deep wells of this region in practically all 

 cases yield a sediment of similar nature. 



X It was impossible to use the Stokes method to identify this substance, for 

 not only was the quantity at our disposal too small but it was mixed with 

 vegetable matter which could not be removed. 



