Professor Epwarp Hutr—On the Nature and Origin of Beds of Chert. OH, 
other districts. Dr. T. Sterry Hunt observes that beds of chert, flint, hornstone, 
and buhrstone, have all apparently been deposited from aqueous solutions.* He also 
shows that silica replaces organic matter in fossils and refers to flint, chert, &c., as 
a proof of the large amount of silica in some waters.t 
Mr. M. ©. White’s observations on the microscopical structure of hornstone 
from the Devonian and Silurian formations of New York, resulted in the discovery 
of numerous forms of Desmidice, also Xanthidie of rare forms, diatoms, spicules of 
sponges and fragments of gasteropods.{ Similar results were obtained from 
observations on the nodules of hornstone from the Black River limestone, and 
that of the Carboniferous beds of Illinois, as shown by F. H. Bradley.§ 
The microscopical structure of true chert, (hornstein), does not appear to have 
been much followed up by continental Petrographers. Except, perhaps in a few 
places the beds of chert are not very largely distributed in the Carboniferous 
Limestone of Europe. In the black chert from this formation from the Plauenschen 
Grund, near Dresden, Ehrenberg discovered diatoms, &c. (“ Mikrogeologie,” XII. 37). 
Those siliceous formations,—such as the berg mehl, tripoli, or polirschiefer, and 
saugschiefer, upon the origin of which by the direct agency of fossil infusoria, this 
distinguished naturalist has thrown so much light, do not come within the scope of 
this paper ; for as we hope to be able to show, the rock here described under the 
term of “Chert,” is due to a transmutation process, and not to any direct organic 
agency. 
The observations of G. Bischof, although not directly bearing upon the formation 
of chert or hornstone in large masses, are interesting, and important in reference 
to the chemical process by which calcareous organisms, may be converted into 
siliceous, The existence of silicified corals in several localities has already been 
noticed, and Bischof points out the peculiar lability of such forms to silicifi- 
cation, owing to the innumerable pores by which the coralis perforated, through 
which waters charged with silica in solution, find their way and deposit the silex. fT 
On the other hand, shells of bivalves, which are seldom found in a silicified form, 
being of more solid construction are less lable than corals to silicification, and 
usually are entirely dissolved away, leaving only the cast.|| He also observes, “ The 
occurrence of quartz, chaleedony, hornstone, &c., in the form of calc spar, proves 
that silica is capable of displacing carbonate of lime.” 
It is doubtful whether the “ hornstein” of German Petrographers is really the 
exact representative of our “ chert.” The description of the microscopic structure 
* Logan, Geology of Canada, p. 574. 
+Chem. and Geol. Essays, pp. 89 and 286, also ‘‘On the Silicification of Fossils,” Canadian 
Naturalist, vol. I., 46. 
+ American Journal of Science, 1862, s. 383, also Annals and Mag. Nat. His. x. 160 (1862). 
tt See also Parr IT, on the chemical similarities of silica and carbon, by Mr. Hardman § /bid. 
|| Elements of Chemical and Physical Geology, Cavendish Hdit. Vol. II., 489. 
q Jbid. Vol. I., 198. 
