204 W. A. Tarr- — Cone-in-Cone. 



A point of much value in discussing the origin is 

 whether the cone-in-cone is dominantly calcite or aragon- 

 ite. Where determinable in the writer's specimens the 

 material is calcite. Cone-in-cone occurs with ferruginous 

 concretions in various localities, hence it is possible that 

 some cone-in-cone is ferruginous, but no cone-in-cone com- 

 posed of siderite has been seen by the writer or reported 

 in the literature. 



Mode of Occurrence of Cone-in-Cone. 



Cone-in-cone usually occurs in shales in association 

 with concretions. It may occur as a layer on the upper 

 side of the concretion, as bands within them, or as a layer 

 on the lower side. The bands within the concretions 

 usually extend from one side to the other, and may be 

 several inches wide. There may be several bands in one 

 concretion. The layers of cone-in-cone above and below 

 a concretion may attain a thickness of several inches, but 

 they usually thin out at the edges of the concretion. 

 Young claims that the cone-in-cone may fold back upon 

 itself, thus forming two bands of cone-in-cone with their 

 apexes pointing toward each other. Such parallel bands 

 are fairly common, but there is no evidence to support 

 Young's view as to the cause of the parallelism. 



The structure may occur as one or more layers, not in 

 association with concretions. The occurrences in the 

 Devonian shales in Pennsylvania, described by Gresley, 

 show three to five layers associated with a band of sand- 

 stone. Such layers may have great variability in plan 

 as well as diverse shapes when seen in section. 



More rarely single layers of calcite showing cone-in- 

 cone may occur within shales. The layers range from 

 one half inch to two and one half inches in thickness. 

 The cone-in-cone may extend entirely across the layer or 

 it may be developed on one side only. 



A very rare occurrence is in coal. Well developed 

 cones from four to six inches high are found in the British 

 coal beds. Their sides are highly polished and slicken- 

 sided. 



