﻿On Cone-in- Cone Structure. 843 



2. ' Some Observations on Cone-in- Cone Structure and their 

 .Relation to its Origin.' By Samuel Rennie Haselhurst, M.Sc, 



f.g.s. 



In a brief review our state of knowledge is summarized, and the 

 deductions of other investigators are analysed. 



The author then outlines the phenomenon of megascopic 

 pseud ostromatism, and certain tectonic features which are 

 always associated with cone-in-cone structure in areas where it is 

 greatly developed. He points to the disadvantage accruing from 

 many observers not having seen it in situ on a large scale, and 

 shows how a simulation of horizontality in stratification masks what 

 he takes to be the key to the diagnosis of this structure. 



Two typical areas are described : — 



(a) The St. Mary's Island-Tynemouth district of the D 5 Coal-Measurea 



of Northumberland. 



(b) The Hawsker-Robin Hood's Bay-Ravenscar district of the North 



Biding- of Yorkshire. 



The specimens collected in these areas are unique, and some 

 dozen types from other areas, including Sandown, Portmadoc, 

 Olney, Somerton, Lyme Regis, and Merivale Park are examined in 

 detail with reference to : — 



(a) Evidence furnished by distorted fossils. 



(&) Chemical composition. 



(c) Geometrical similarities. 



(cZ) Microscopic structures. 



The author critically examines^ the accepted hypothesis that 

 cone-in -cone structure is something essentially due to 

 crystallization. 



He describes the results of some high-pressure mimetic experi- 

 ments, aided by a Royal Society grant which he now gratefully 

 acknowledges. These experiments were designed to produce this 

 structure, and reveal what the author believes to be man}'" new 

 points on the origin of concretions and cone-in-cone in particular. 

 The experiments are new, inasmuch as the media used, namely : 

 brittle, semi-plastic, and plastic, are enclosed in tunics of varied 

 design, and then subjected either to a high uniform hydrostatic 

 pressure or to a direct thrust. The results are in many ways 

 analogous to those of Ewing, Goodman, and Daubree who, it is 

 remarked, did not attempt to explain cone-in-cone structures. 



The author concludes from the evidence : 



(i) that cone-in-cone is not due to crystallization, but is a mechanically 

 produced structure due to great and localized pressure ; 



(ii) that it is closely allied to the phenomenon known as pressure 

 solution; 



(iii) that cone -in -cone structure is closely associated with other rock- 

 structures which are mutually indicative the one of the other, and 

 also of their mode of origin. 



