E. O. Hovey — Cherts of Missouri. 403 



the, cherts as well terminated crystals of some size more or 

 less completely filling cavities in the chalcedony, as drusy 

 coatings to cavities, and as well rounded grains which may or 

 may not form the nuclei of spherules. The crystallized quartz 

 seems to be secondary to the chalcedony in its deposition, or to 

 form the last phase in the aggregation of the cherts, the latter 

 appearing to be the case where seams of coarsely granular 

 chalcedony grade into lenses of finely granular or crystallized 

 quartz. The strictly secondary quartz lines or fills cavities in 

 the chert without having any apparent connection with the 

 chalcedony. The rounded grains are evidently quartz sand 

 which has been caught within the chalcedony as it was deposit- 

 ing or aggregating. From the frequent occurrence of inclu- 

 sions in them they are probably granitic in their origin, and 

 this view is strengthened by the rare presence of a grain show- 

 ing the multiple twinning lamellae of microcline. Dr. C. R. 

 Keyes* describes cherts from the Lower Carboniferous (Bur- 

 lington) of the northeastern part of the State which " upon 

 exposure to the weather quickly slacken like quicklime to a 

 fine, intensely white powder." This would indicate that the 

 silica in them was amorphous, but specimens of this character' 

 were not sent the writer. Scattered through all the slides 

 there are minute irregular scales and specks of a yellowish 

 brown to black substance which may be referred to amorphous 

 iron oxide (limonite) though some of them are more probably 

 grains of magnetite. A noteworthy feature of most, if not 

 all, of the thin sections, is a " dusty " appearance as seen in 

 ordinary light. This dust disappears to a considerable extent 

 when the light is cut off from the upper side of the section. 

 The phenomenon may be due to clayey matter present in the 

 rock. In view of the discovery by Professor H. A. Nicholsonf 

 and Dr. G. J. Hinde^: of radiolaria in chert from the Lower 

 Silurian (Ordovician ) strata of Scotland, and by Professor 

 W. J. Sollas§ and Dr. Hinde,]| of sponge spicules in Carbon- 

 iferous chert from Ireland, very careful search was made 

 through these Missouri cherts for indications of anything of a 

 similar nature. Nothing whatever of this kind was found, 

 with the possible exception of some slender cylindrical rods in 

 a specimen from the Lower Carboniferous at Webb City in 

 Jasper County. The rods are noticeable in cavities in the 

 rock, and the one which was measured was 2 ram long by 012 mm 

 in diameter, but it seemed to have been thickened by some 



*This Journal, III, xliv, 451, 1892. 

 f Trans. Edinb. Geol. Soc, vol. vi, pt. 1, p. 56, 1890. 

 % Ann. and Mag. Nat. Hist., VI, vol. vi. p. 40, 1890. 

 § Ann. and Mag. Nat. Hist., V, vol. vii, p. 141, 1881. 

 J Geol. Mag., N. S., Dec, III, vol. iv, p. 435, 1887. 



Am. Jour. Sol— Third Series, Vol. XLVIII, No. 287.— Nov., 1894. 

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