THE CHERT ROCKS OF SUBCARBONIFEROUS KANSAS. 671 



beds of the streams, Crinoids seem to be the most abundant, but many other 

 types are represented. The shells of the crinoids are rarely present, but the 

 cavities from which they have been removed so perfectly represent their out- 

 lines that their forms are plainly shown. There is, however, quite frequently a 

 central stem of silica corresponding to the central cavity of the crinoid stem. 

 They have been so numerous that it is easy to find blocks of chert that will not 

 weigh more than half as much as an equivalent volume of solid chert. Speci- 

 mens are sometimes found which show that a portion of the rock was formed 

 without including shells, while the other portion of the same specimen was liter- 

 ally filled with them. 



In some places the chert presents quite a tufaceous appearance. This is 

 best represented at the Short Creek mines, although it is by no means confined to 

 that locality, many similar specimens having been found on the west side of the 

 river. At Short Creek hundreds of tons of this partly decomposed chert have 

 been lifted from the mines. In many cases the outlines of the fossils are still 

 easily detected. Also it is not uncommon to find inclosed crystals of sphalerite 

 (zinc blende), or cavities from which such crystals have been dissolved. It was 

 an easy matter to select a series of specimens, showing all the variations, from 

 those in which the crystals were almost perfect to those from which they had been 

 entirely removed. 



In such a series, it is to be noted that the decomposition of the rock itself 

 corresponds almost exactly with that of the sphalerite crystals ; that is, the rocks 

 which contain the most perfect crystals are the least decomposed, while those 

 from which the crystals have been entirely remo^ved, have suffered the greatest 

 decomposition. 



Another peculiarity of the chert is the fact that it has innumerable fractures 

 running in every direction. In some places they are quite a distance apart, in 

 others they are very close together. In some places great masses of it seem to 

 have been broken into millions of fragments without any of them being remov- 

 ed; in other places the angular fragments seem to have been partially removed 

 and subsequently formed into conglomerates by the cementing action of calcite, 

 dolomite, iron oxide or zinc blende. 



For two reasons I have thus detailed facts which can be observed by all. 

 First, it is thought that Southeastern Kansas is not only the most intricate, geolog- 

 ically, but also the most interesting of any part of the State. Second, the facts 

 mentioned may have a bearing on theoretical geology. 



Three hypotheses have been offered to explain these phenomena. First, all 

 of the rocks except the conglomerates were originally limestone. In the course 

 of time waters charged with silica, or a silicate, metamorphosed portions of the 

 limestone, leaving them in their present condition. Previous to this action, cav- 

 ities had been worn in the limestone in which the silica-laden waters deposited 

 silica, forming the concretions. In some places the limestone has been subse- 

 quently removed, leaving the concretions free ; in other places they have been 



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