W. A. Tarr—Cone-in-Cone. 199 



Akt. XX. — Cone-in-Cone; by W. A. Tabr. 1 



Cone-in-cone is a structural feature found in shales and 

 rarely in coal. It is usually associated with concretions 

 but not necessarily so. An occurrence of cone-in-cone in 

 coal and its development in bands of calcite are such 

 exceptions. The cone-in-cone structure consists of a 

 series of cones within cones, adjacent cones uniting to 

 form lenses or layers. When associated with concre- 

 tions the cone-in-cone may occur on the upper or lower 

 surface, or, more rarely, within the concretion. 



The structure was recognized and called cone-in-cone 

 in the early part of the last century. It was not so called 

 by all, however. Hildreth, in 1836 (see literature at end 

 for all references), described it as a "fossil columnar 

 Madrepore." It has also been called "cone-in-cone 

 coral." The "German name for cone-in-cone is "tuten- 

 mergel" and was given to it as early as 1823. 



Cone-in-cone has been described by Marsh, Sorby, New- 

 berry, Jukes, Dawson, Daintree, Young, Sach, Garwood, 

 Gresley, Broadhead, and many others. Their descrip- 

 tions are all very similar, although their conclusions 

 regarding the origin of cone-in-cone differ considerably. 



Probably the majority of investigators have regarded 

 cone-in-cone as having been caused by pressure which 

 was due (since the structure is so frequently seen in asso- 

 ciation with concretions) to the expansion of concretions 

 through growth. Thus, most cone-in-cone structures are 

 regarded as of secondary origin. Some of those holding 

 this view are Marsh, Geikie, Dana, Gresley, Grimsley, and 

 Chadwick. Others have regarded the structure as being 

 due to crystallization or to "imperfect crystallization." 

 Owen, Newberry, Geikie, Sach, Grabau, and Keyes have 

 advocated one or both of these methods. 



Odd suggestions have been made by Sorby, who sup- 

 posed that oolites had formed the sides of the cones ; by 

 Daintree, who believed the cones were chemical precip- 

 itates ; and by Young, who says unequivocally, that they 



1 The writer -wishes to acknowledge his indebtedness to many friends for 

 material furnished for this study. Mr. H. L. Griley and W. H. Twenhofel 

 have furnished some excellent material. The late G. C. Broadhead collection 

 at the University of Missouri contained several excellent small specimens. 



