Editorial Comment. 117 
with the polariscope shows the structure to be non-crystalline. 
Prof. Hitchcock, to whom specimens were referred by Dr. 
Andrews director of the chemical labqratory of the University 
of Iowa, finds a considerable portion of the chert to consist of 
"soluble silica." All silica, however, is soluble under certain 
conditions; and all the facts at present in our possession, point 
to the conclusion that the chert in the Upper Coal Measures of 
Iowa was deposited from the solution in sea-water after the 
limestone beds, with their multitudes of Fustdina shells, had 
been laid down. The process was one of pseudomorphism. 
Something, we cannot tell what, determined that at certain 
poixits in the limestone beds the percolating waters, charged 
with silica, took into solution the more soluble calcic carbonate 
and deposited an equivalent amount of silica in its place. Each 
such point became a center around which the process of ex- 
change proceeded, until masses of chert varying in shape and 
in dimensions from a fraction of an inch to more than a foot in 
diameter were formed. The sedimentary particles of the lime- 
stone and the calcareous shells of Fusulina were involved in a 
common process. 
THE NEW GEOLOGICAL MAP OF EUROPE. 
We would like to emphasize the request of Dr. Frazer, sec- 
retary of the American committee of the International Congress 
of Geologists, that American geologists should enable him to 
report the entire subscription of 100 copies of the geological 
map of Europe now being constructed by the International 
Congress. All institutions in which geology is taught in the 
progressive methods and spirit of the day will subscribe for it, 
and all others are earnestly advised to. 
BULLETIN OF DENISON UNIVERSITY. 
We have received the bulletin of the scientific laboratories 
of Denison University at Granville, Ohio. This is the sec- 
ond volume, and is brought out under the joint superinten- 
dence of Profs. Herrick and Cole. It opens with a sketch of 
the geological history of Licking county, Ohio. This is fol- 
