W. A. Tarr—Cone-in-Cone. 211 



would then become a very important factor. The cones 

 formed in coal were certainly due to pressure unaided 

 by solution. 



The other method by which a conical shape might be 

 induced hinges upon the original form of the calcium 

 carbonate being aragonite and subsequently altering to 

 calcite. Conceivably this alteration, being brought about 

 by water, would start along the joint in a bed of cone-in- 

 cone and proceed inward. As the aragonite changed to 

 calcite there would be a volume increase and expansion 

 of the outer portion, leaving a suggestion of a cone on 

 the interior. How effective this would be is problemati- 

 cal ; very likely the effect would be slight. 



But a combination of the above factors could very well 

 give rise to the cone-in-cone structure. The radial aggre- 

 gates, when acted upon by pressure, would favor the 

 development of fractures along which solutions might 

 enter, dissolve, and remove material, thus permitting 

 further movement. Artificially formed cones, taken in 

 conjunction with the fact that a majority of cone-in-cone 

 occurs in layers of radial fibers, lends strong plausibility 

 to this suggestion. 



The development of cone within cone might conceivably 

 be accomplished in the following manner. Solutions 

 entering along a joint might convert the aragonite to 

 calcite. This change would progress inward from the 

 joint a variable distance, where another fracture plane 

 would develop by the expansion of the material in chang- 

 ing from aragonite to calcite. Thus a series of cones 

 might be formed, one within the other. Another method 

 has been indicated above, that is, pressure producing a 

 series of minute cracks on the base of a cone. These 

 were parallel to the circumference of the base and con- 

 tinued pressure might easily have started another cone 

 within the first. But the most probable method would 

 seem to be by means of the radial structure of the calcite. 



Was the Material Originally Aragonite? 



Reference has been made so frequently in the above, 

 discussion to the possibility of the calcite having been 

 originally aragonite that it would seem well to summarize 

 the reasons for believing that this may have been the case. 



