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IOWA ACADEMY OP SCIENCE 
His general conclusion is that the cherts are due to chemical precipitation, 
probably at the time of the deposition of the strata in which they occur, or 
before their consolidation. No good evidence of the existence of silica secreting 
organisms was found by him in the cherts. 
Buckley and Buehler- regard the chert of the Burlington and Keokuk lime- 
stones of southwestern Missouri as being in part an original precipitate and in 
part a secondary product resulting from the silification of the limestone. By 
them the fossiliferous chert is thought to have been deposited contemporaneous- 
ly with the limestone, while the chert which contains fossils is regarded as a 
replacement product. 
The evidence gathered by the writer during his investigation of the cherts 
of this area supports the view that the material has resulted entirely from 
the replacement of the limestone. The fossiliferous nature of much of the 
chert and the gradation of chert through siliceous limestone to pure limestone 
substantiates this view. Furthermore, the irregularity and discontinuity of 
the chert bands and nodules argues strongly against any theory which regards 
the chert as original. The evidence of the secondary nature of the chert is 
also strengthened by the occurrence of isolated patches of limestone completely 
surrounded by chert. Such remnants clearly suggest a former continuity of 
the limestone. 
The time of the replacement of the limestone is not well known, but it is 
believed that the process must have proceeded contemporaneously with the re- 
crystallization of that rock. 
The source of the silica is a matter of conjecture. Little is known, as yet, 
concerning the possible existence of silica secreting organisms in the Osage seas. 
Microscopic study of several thin sections of chert from the Burlington and 
Keokuk formations revealed the presence of a few sponge spicules in only one 
sample. It is probable, therefore, that much, if not all, of the silica is of in- 
organic origin, having been deposited in a colloidal condition upon the bed of 
the sea while the limestone, was being formed. 
BIBLIOGRAPHY. 
1. HoveTj E. O. (1894) A study of the cherts of Missouri. Mo. G'eol. Surv., vol. 7, 
pp. 727-739. 
2. BuckleYj E. R. and Buehler, H. A. (1905) Mo. Bur. of Geol. and Mines, vol. 
4, 2d series, pp. 37-40 and pp. 50-52. 
