460 S. Calvin—Shale at Independence, Towa. 
Art. LXIX.—On some dark Shale recently discovered below the 
Devonian Liimestones at Independence, Iowa; with notice of the 
Fossils at present known to be in it; by S. Canvin, Professor 
of Geology, State University of Iowa. 
THE Devonian deposits of Iowa, as now known, may be 
roughly represented by the annexed diagram, in which 1 indi- 
cates the position of a member of the 
3 | group recently discovered at Independence, 
consisting of dark argillaceous shales wit 
2| some thin beds of impure, concretionary 
limestone. It has been explored to a depth 
1| of twenty or twenty-five feet. No. 2 
represents all of what is usually included 
under the head of the Devonian limestones of Iowa, and is 
made up largely of limestone with some associated beds of 
light-colored shales ; estimated thickness, 150 feet. No. 3 isa 
od of argillaceous shales exposed at and near Rockford, Iowa, 
and is referred to frequently as the Rockford Shales. It 
abounds in fossils, and weathers, on exposure, into a stiff clay 
that has been utilized in the manufacture of brick; observed 
thickness, seventy feet. 
Until recently, Nos. 2 and 3 of the above section were sup- 
pest to make up the entire thickness of Devonian rocks in 
owa. No. 2 not only varies, as already indicated, in lithologi- 
cal characters, but the grouping of fossils differs widely in 
equivalent of the New York Chemung. On the other hand, Dr. 
C. A. White, Geology of Iowa, 1870, vol. i, p. 187, is of opinion 
