THE CHERT ROCKS OF SUBCARBONIFEROUS KANSAS. 675 



It seems but reasonable, then, that large portions of silica were precipitated 

 as gelatinous silicic acid which gradually settled to the bottom and formed great 

 chert layers. There would not be pure silica unless the waters were free from 

 impurities, neither would the limestone formed be free from flint unless the 

 •waters were periodically entirely free from silica. Let us recall the condition in 

 \\ hich these rocks are now found in southeastern Kansas. The regular [strati- 

 fication in places alternating with limestone which was forming at the same geo- 

 logical time, just as it should be. Also the presence of fossils would be expected, 

 some of them being silicified, others resisting this action, to be subsequently 

 removed by waters charged with carbonic oxide. 



The concretionary formations with their banded structure might also have 

 been expected; and finally the irregular deposits which have been called ''disc 

 shaped" would certainly be formed where there was not enough silica to form 

 continuous layers. As far as observed, everything seems to be just as one would 

 expect. The writer looks upon the peculiar formations described as evidences 

 which may be added to that of the sandstones composed of crystallized grains. 

 The amount of silica included in the chert and sandstone beds of different eras is 

 so great that anything short of direct precipitation and crystalHzation from satu- 

 rated solutions, seems to him intirely inadequate as a cause. 



The tufaceous appearance of some of the rocks is evidently due to the sol-, 

 vent power of water. Dr. Schmidt, of St. Louis,* thinks that these are of much 

 more recent formation than the others; that the limestone was first dissolved and 

 the cavities filled with porous chert. This view is inconsistent with the occur- 

 rence of fossils in these rocks. If the limestone had been dissolved out, the fos- 

 sils would have been destroyed, so that the subsequent formations in the cavities 

 thus produced would have been entirely barren of fossils. They also contain 

 zinc crystals as occasionally do the undecomposed rocks, which would further 

 indicate that they were of the same age. 



What already has been said will show that these rocks cannot be of volcanic 

 origin, as has been held by Prof. Hay, of Chetopa, Kansas. The occurrence of 

 fossils alone is sufficient to disprove this theory, but the additional evidence of 

 the enclosed crystals place it beyond all doubt. If we consider the great range 

 of temperature between the fusing points of zinc sulphide and silica, it is seen at 

 once that the idea of the two having cooled from a molten mass is entirely unrea- 

 sonable. The fractures in the chert beds remain unexplained. Dr. Schmidt, as 

 .above referred to, attributes them to' the contraction caused by the dolomitization 

 of the limestone and the dislocations caused by the dissolving out of the lime- 

 stone in places. This view is objectionable for two reasons. First, the decline 

 of the old theory that pure limestone is dolomitized on a grand scale. With our 

 present knowledge of the chemical properties of the salts of calcium and magne- 

 sium it seems much more reasonable that the magnesium now present in the great 

 beds of limestone in the Mississippi Valley was enclosed in their formation. 

 Second, if the old theory be true, the assigned cause is entirely insufficient. 



■> Trans. St. Louis Acad. Sci., Vol. 3, No. 2 p. 246. 



