IOWA ACADEMY OP SCIENCES. 
75 
NOTE ON THE NATURE OF CONE-IN-CONE. 
BY CHARLES R. KEYES. 
Cone in- cone is a term which has been applied more or less 
widely to a peculiar structure often found in beds of shale. 
Ordinarily it appears in thin sheets or layers, from three to six 
inches in thickness. The bands have a more or less well- 
marked columnar structure, each column being* about half an 
inch in diameier and composed of a series of small conical seg- 
ments set one within another. In general appearance frag- 
ments resemble the familiar coral Lithosbrotion. 
Much has been written on the origin of cone-in-cone, and 
numerous and widely different explanations have been offered. 
So far as I know, none of these numberless attempts to account 
for this peculiar structure appear to be satisfactory expositions 
of the true cause of the formation. 
Recently there have been obtained in Marion, Boone and 
Webster counties, in this state, some unusually instructive 
examples which offer, I believe, a correct solution to the prob- 
lem of origin. These specimens range from a black, opaque, 
clayey variety — the common form — through all gradations to 
a white, translucent kind. The latter is found to be made up 
of numerous long, often needle-like crystals and flat plates 
which radiate from a center — the apex of the cone — new nee- 
dles coming in as rapidly as the spaces between those near the 
center become large enough to admit them. Chemical analysis 
shows that this variety is nearly pure calcic carbonate, in a well 
crystalized form. Analysis of the more earthy kinds also show 
a high percentage of lime. The results of examinations by 
Prof. G. E. Patrick are as follows: 
I. Clear variety from Madrid 98.36 per cent Ca CO 3 
II. Clayey variety from Fort Dodge 83.12 per cent Ca CO 3 
As the clear cone- in- cone acquires more and more clayey 
matter the crystals of calcite gradually lose their mineralogical 
