172 
IOWA ACADEMY OF SCIENCE Voi.. XXVII, 1920 
siliceous nodules were found in the chalk of England and called 
flint while later, and elsewhere, siliceous nodules in the limestone 
were found and called chert. It appears that authorities such as 
A. W. Grabau, A. J. Jukes-Brown, Lake & Rastall, J. S. Flett in 
the Encyclopaedia Britannica, and Pirsson and Schuchert to a 
certain extent propose to draw a hard and fast line between the 
two substances, depending on their occurrence in chalk or in lime- 
stone. So far as present knowledge is concerned their origin 
is professedly uncertain, A. C. Trowbridge and E. W. Shaw in 
the “Geology and Geography of the Galena and Elizabeth 
Quadrangles” (Illinois State Geological Survey, -Bull. 26, 1916, 
pp. 80-81) state the case by pointing out that the origin of cherts 
and chert bands is entirely problematical. Therefore it seems 
altogether out of place and quite confusing to base, simply for 
the sake of apparent exactness, a precise distinction on mode of 
occurrence when, in all possibility, flint and chert may be found 
subsequently to have identical origins and thereby cause the terms 
to be synonymous. 
In the second 'place come the physical characteristics of flint 
and chert, their composition and the limitations to surround the 
use of the terms. Confusion appears to have arisen by attempting 
to assign minor differences to each. On the whole the color varies 
from almost white through gray and brown to black, the hardness 
is that of quartz or slightly different owing to impurities, and the 
fracture is conchoidal. As to texture the silica has been described 
as amorphous, or cryptocrystalline, or coarsely crystalline, or a 
mixture of the first two. Limitations should be applied here since 
the use of chert for coarsely crystalline silica will infringe sooner 
or later on the field of quartz itself and will meet obvious difficul- 
ties. Such admittedly is its misuse as intimated in the citation 
from C, K. Leith. Concensus of opinion, however, tends to re- 
strict the terms to cryptocrystalline and amorphous varieties of 
silica. Another stumbling block lies in the composition as related 
to texture which relation is given as impure quartz, or crystalline 
silica, or amorphous and hydrous silica, or a mixture of crystal- 
lized silica and non-crystallized silica with a little chemically 
combined water. Mineralogists, as Dana, Kraus, Miers, Moses 
and Parsons, Crosby, and Phillips include both flint and chert 
under the anhydrous varieties of the oxide of silica. 
The entire confusion seems to result solely from the uncertainty, 
warranted no doubt, that envelops the terms. The fact stands out 
that they are blanket terms which, in the present state of knowledge 
