W. A. Tarr—Cone-in-Cone. 205 



Distribution of Cone-in-Cone. 



Geo graphic ally cone-in-cone structure has been 

 reported in various places in the United States. The 

 localities first noted were those in western New York, 

 Pennsylvania, and Ohio. Other localities are in Michi- 

 gan, Illinois, Iowa, Missouri, Texas, Kansas, Nebraska, 

 South Dakota, Wyoming, Montana, Colorado, Utah, and 

 California. (The writer's collection includes specimens 

 from the states in italics.) It is probable that the struc- 

 ture is more widely distributed than is indicated above, 

 for its occurrence is only mentioned incidentally in most 

 of these cases and there is usually no reference to it in 

 the index of the reports. It is known to be rather widely 

 distributed in England, France, and Germany. 



Geologically there is apparently nothing significant 

 about the geological occurrence of cone-in-cone structure. 

 It has been reported in middle Cambrian beds in Utah. 

 It occurs in the Devonian in New York, Pennsylvania, 

 Ohio, and Michigan. The Pennsylvanian in Illinois, 

 Iowa, Missouri, and Kansas has furnished numerous 

 specimens of cone-in-cone. The Permian in Kansas, 

 Montana, and South Dakota, and the Eocene in Texas 

 have been found to contain the structure. In Europe it 

 has been found principally in the Carboniferous and the 

 Jurassic formations. 



Origin. 



The published views regarding the origin of cone-in- 

 cone are extremely vague. Pressure is regarded by some 

 as a factor, but why pressure should produce cone-in-cone 

 is not explained. The presumption is that pressure in 

 forcing the material of the structure through the adjacent 

 rock produced cones. Crystallization is also suggested, 

 but why it should develop cones is again not explained. 

 Many minerals are known which may crystallize in radiat- 

 ing masses, but such masses are spherical, or closely 

 related forms, and not conical. It is not clear- why 

 crystallization should develop only a fraction of a sphere 

 and do it as perfectly as has been done in the case of 

 cone-in-cone. 



The following suggestions represent the conclusions to 



