IOWA ACADEMY OF 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 Lithosfcrotion. 



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 specitnens 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: 



1. Clear variety from Madrid 96.36 per cent Ca CO3 



II. Clayey variety from Fort Dodge 83.12 per cent Ca CO3 



As the clear cone- in- cone acquires more and more clayey 

 matter the crystals of calcite gradually lose their mineralogical 



