W. A. Tarr — Cone-in-Cone. 



201 



The height of the cones varies from a thirty-second of 

 an inch to eight or nine inches. Those from one to four 

 inches in height are the most common. The diameter of 

 the base depends upon the height and upon the angle of 

 slope of the sides of the cones. In many cones this 

 diameter is nearly equal to the height of the cone. The 

 included angle (a, fig. 2) at the apex of the cone ranges 

 from 25° to 70°. If the cone is well developed this angle 

 is generally 60° to 70°. Partially developed cones are 

 sharper. 



Fig. 3. 



Fig. 3. — Cones along a plane. 



The sides of the cones are rarely perfectly smooth. 

 Striatums such as are seen on slickensided surfaces are 

 common. What Gresley calls " conic scales" (fig. 5) are 

 also very common. The sides of the cone may be ribbed 

 or fluted, thus giving a notched outline on the base (fig. 6). 



Fig 



Fig. -i. — Concretion with layer of cone-in-cone (scale 1 inch equals 1 foot). 



The inside of a cone into which another cone fits is 

 always ribbed with circular rings, which are darker in 

 color than the material composing the mass of the cone- 

 in-cone (fig. 7). These rings are always on the inside of 

 the cone. They vary in width from mere lines to over 

 one quarter of an inch. Within a given cone they are 

 very fine near the apex, and coarsest near the lower edge. 

 This holds true for all specimens examined by the writer 



