W. A. Tarr—Cone-in-Cone. 207 



have been enabled to move because of the solution of the 

 material previously occupying the space between the 

 small cone and the large one. This would be the material 

 in the shaded area in figure 11. The removal of this 

 material m solution would enable the cone to penetrate 

 the larger cone. 



Fig. 11. 



Fig. 11. — Shaded area shows the material removed in solution, to permit 

 the movement of the inner cone. 



The rings of dark clay on the interior of the cone cup 

 have lost all their carbonate content and represent merely 

 the insoluble residue obtained by dissolving the material 

 composing the cone. A careful study of these rings 

 showed that they contained more material near the base 

 of the cone, due to the fact that more carbonate material 

 has been removed by solution from that portion of the 

 cone. The ring of dark clay occupied a depression on the 

 inside of the cone cup. These depressions may be one- 

 eighth inch or more deep, and are separated from each 

 other by a thin partition of calcite (fig. 8, B). The ring 

 of clay fits into this depression. 



The facts cited above prove that movement and solu- 

 tion have taken place during the development of the cone- 

 in-cone structure. The conclusion may be drawn that 

 the movement certainly involved some pressure, and as 

 material was removed by solution the cone slipped down 

 (or up) inside the larger cone. 



Source and amount of the pressure — It can hardly be 

 doubted that some pressure was involved in the formation 

 of the structure. This pressure probably was not large, 

 because most occurrences of cone-in-cone were never 

 deeply buried. Many have thought that the pressure, 

 where the cone-in-cone was associated with concretions, 



Am. Jour. Sci.— Fifth Series, Vol. IV, No. 21. — September, 1922 



14 



