W. 8. Gresley — On " Cone-in- Cone" Structure. 19 



Fig. 2 will probably better explain what is intended to be noticed 

 above. It represents a portion of a vertical section of one of the 

 master cones enlarged about four times. The specimen is from a 

 bed of clay-ironstone occurring above the fire-clays of the Western 

 division of the Leicestershire Coal-field — a horizon which has 

 furnished the writer with more than one illustration of the way in 

 which cone-in-cone structure occurs. 



But further, I would point out that the concentric serrations 

 between the cones, and shown as adhering to the exterior surface of 

 one of them at c, Fig. 2, are also composed of scaly or semi-cone-in-cone 

 structure. This, though of minute development, can readily be 

 detected with a pocket lens, especially upon partially weathered 

 samples. The bases of these tiny flakes seem to terminate against 

 the serrations of the master cones, and upon the sides of the cone- 

 structure forming their walls (see Fig. 2). In short, this specimen 

 (and doubtless it is a typical one) appears to be wholly built up of 

 ' cone-in-cone,' of at least three separate and distinct developments, 

 a, h, and c. For this curious three-fold structure I fail to see how 

 the ebullition-of-gases theory can satisfactorily account. 



With reference to the question of cone-in-cone found upon the 

 under as well as the upper surface of a stratum or a concretionary 

 mass, Mr. Young would have us believe that when this does occur 

 it has pi'obably been due to the shrinkage of the mass, such contrac- 

 tion having actually carried the coned surface round to the underside. 

 I think the following instances of reversed or double cone-in-cone 

 at once upset his theory. 



(b) In a stratum of blue shale or ' bind ' at the village of Donis- 

 thorpe in the Leicestershire Coal-field, occur some large concre- 

 tionary masses — often several tons in weight — of hard and compact 

 fine-grained siliceo- ferruginous sandstone, locally called ' cank,' whose 

 upper and lower surfaces are often largely covered with cone-in-cone 

 formation. That upon the under surface, however, is always the 

 most feebly developed. Now, as the coned surfaces are always most 

 strongly formed in the centre of the mass, or, in other words, as the 



edges towards b h (see Fig. 3, which represents a transverse section) 

 are almost devoid of cone structure, it is at once apparent that the 

 cones upon the under side cannot have been brought into their pre- 

 sent position by any known process of shrinkage or curling up, or 

 downwards, of the nodules. Besides, in one instance, we have at a, 



