212 W. A. Tarr — Cone-in-Cone, 



1. The cone-in-cone is always found in material of fibrous 



form, a structure more common to aragonite than calcite. 



2. The fibers are dominantly radiating, also a common 



arrangement for aragonite. 



3. Aragonite easily alters to the paramorph calcite. 



4. The change from aragonite to calcite involves a volume 



increase of 8.35 per cent, a change that would give a 

 marked pressure, and pressure has been involved in the 

 formation of the cones. 



5. Radial aggregates with pinacoidal cleavage (both common 



in aragonite) would be favorable factors in the formation 

 of the cones. 



6. Aragonite is more readily soluble in groundwaters than 



calcite. 



7. The combination of factors given above would hardly be 



fortuitous. 



Conclusions. 



Cone-in-cone is best developed in shales and is gener- 

 ally composed of calcinm carbonate in the form of calcite, 

 it having been originally, possibly, aragonite. The cal- 

 cium carbonate always contains more or less argillaceous 

 material. Studies show that there must have been some 

 movement in the development of the cone structure and 

 also that a certain amount of solvent work had taken 

 place. The insoluble material in the calcite is left behind, 

 through the removal of the calcium carbonate, and forms 

 the rings of material (usually dark) which are seen on 

 the interior of all cones that are well developed. The 

 fibrous structure of the calcium carbonate has favored the 

 parallel arrangement of the rings within the cone. 



The cones are probably the result of pressure due to 

 (1) weight of overlying sediments, (2) growth of concre- 

 tions, (3) (the most important) an increase in volume due 

 to the change of aragonite to calcite, acting in connection 

 with the radial or parallel arrangement of the calcium 

 carbonate fibers ; and to solution, which became effective 

 when the pressure had induced the first crack in the layer, 

 groundwater entering and removing the material along 

 this joint. The removal of material along this fracture 

 permitted the further movement of cone within cone. 



Mineralogical Laboratory, 

 University of Missouri, 

 Columbia, Mo. 



