W. S. Greski/ — On " Cone-in- Cone" Structure. 



21 



into the cone-in-cone formation on the one hand and disappearing in 

 the opposite direction, namely : — towards the periphery of the nodule 

 (see Fig. 5). 



i^l*'^ 





2o, 



A peculiarity in the appearance or arrangement of this spherulitic 

 structure is that the surface of it often takes a beautiful wavy or 

 fantastic stalagmitic form, giving the idea that the substance of the 

 structure was in a semi-fluid condition during formation of the 

 botryoidal structure. The aspect is not altogether unlike a number 

 of flat bunches of very small grapes, disposed in more or less regular 

 rows or terraces one above another (see Fig. 6). The globules or 

 spheres forming the apices or lowest points of these little wavy ridges 

 are always the largest or most perfectly developed of the individual 

 groups or bunches. These tiny spheres contain a considerable per- 

 centage of lime, as do the cone-in- cone masses which are encircled 

 by them. 



With respect to the mineral constituents of cone-in-cone rock, 

 Mr. Young seems to hold that calcareous matter was essential to its 

 existence. As many of my specimens are not afiected by the acid 

 test, the lime, if originally present, has been since removed. 



It ma}' be interesting to remark here, that cone-in-cone structure 

 occurs in the Upper Cambrian rocks — the Skiddaw slates — near 

 Shap. Were it necessary, I could instance other interesting examples 

 of cone formation, but from what has been said it will be obvious that, 

 notwithstanding my admission of Mr. Young's perseverance and care 

 in having worked out so much and given a very reasonable explana- 

 tion of cone-in-cone, which, had it not been for the discovery of the 

 double and the complicated instances, I should certainly liave ac- 

 cepted as the probable correct one, I am compelled to discard it as 

 not being sufficient to account for all the observed facts. 



It is exceedingly improbable that this kind of cone-in-cone struc- 

 ture can have been formed in one way as regards the upper layers of 

 it ; and in another way as to those found with their bases pointing 

 downwards. I myself have no explanation to advance. The struc- 

 tures observed are, however, very complex, they seem to deserve a 

 closer examination than they have yet been subjected to, not in the 

 field only, but in the laboratory and also microscopically. 



Fig. 1, natural size. Vertical section of portion of three 'master' cones. 



Fig. 2, x 4. Enlarged view of part of a ' master ' cone. a. showing the cone 

 structure in its walls, b. and c. the semi-cone formation of the clay serrations on 

 the back of the ' master ' cone. 



