part 1] or the shales- with-' beef.' 93 



crystallization around an axis, instead of a point as in the latter. 

 Of this arrangement, however, the cones in ' beef ' show no sign. 

 O. C. Marsh l considered growth-pressure as the chief factor. 

 Prof. J. A. Gr. Cole ~ rejected this view, and adhered to that of 

 Sorby, remarking that ' the so-called beef . . . forms the best link 

 I am acquainted with between cone-in-cone and ordinary Hbrous 

 crystallization ' (oj). cit. p. 140). Prof. T. Gr. Bonney 3 allowed a 

 greater part to the mechanical element, and considered contraction 

 following crystallization to be an essential cause. Finally, O. M. 

 Reis 4 dealt with the subject at great length. He considered that 

 long-continued concretionary crystallization of calcium-carbonate 

 solutions in argillaceous strata, under some pressure and aided by 

 decaying organic matter, is the principal condition. Contraction, 

 re-solution, and deposition help in the production of some of the 

 complex effects. 



Now, cone-in-cone is evidently a primary structure in 'beef- 

 veins, and not the result of forces that disturbed the strata. 

 Occasionally, fossil shells may be found along the parting ; but 

 there is nothing to indicate that exceptionally complex structures 

 are associated with richness of organic remains. Moreover, the 

 hbrous character of ' beef ' suggests rapid, not 'long-continued' 

 crystallization ; and, finally, the close packing and the mutual 

 interference of the fibres during growth are evidence that con- 

 traction cannot have taken place. 



There seem to be only three essential facts bearing on the origin 

 of cone-in-cone structure : namely, (i) its limitation to fibrous 

 or acicular calcite ; (ii) the direct increase of complexity with 

 thickness; and (iii) the penetration of a 'beef '-vein as a whole 

 by the cones, with a total disregard of the internal structure. 

 1 shall endeavour to show that the sensitiveness of the calcite-fibres 

 to shear-stresses set up during their crystallization is responsible 

 for these peculiarities. 



In the first place, it is apparent that during crystallization the 

 'beef-veins must have supported a load equal to the weight 

 transmitted by the overlying deposit, less the tensile stresses 

 originating through desiccation. If, now, the stability of, an 

 element from the middle of a growing ' beef '-vein be considered, 

 this load will produce a principal (vertical) stress p acting on the 

 top and bottom faces of the element (fig. 8, p. 94). In addition, 

 there will be two equal principal (horizontal) stresses q acting on 

 the vertical faces of the element, and generated by the resistance 

 to lateral growth set up by the crowding of the fibres. (Only one 

 of these principal stresses appears in the figure, for the other acts 

 normally to the plane of the paper.) Now, stress on any plane 

 inclined to the principal stresses is oblique, and there is some 



1 Proc. Amer. Assoc. Sci. 1867. 



2 Min. Mag. vol. x (1892) pp. 136-41. 

 :! Ibid. vol. xi (1895) pp. 24-27. 



* Geognostische Jahreshefte, 1902 (1903) p. 250. 



