Vol. 50.] CONE-IN-CONE IN THE ' DEVONIAN ' SERIES. 731 



43. Cone-in-cone : How it occurs in the ' Devonian ' Series in 



Pennsylvania, U.S.A., with further Details of its Structure, 



Varieties, etc. By W. S. Gresley, Esq., F.G.S. (Read 



May 9th, 1894.) 



[Abridged.] 



[Plates XXXV. & XXXVI.] 



The objects of this communication are : — (1) to clearly demonstrate 

 that cone-in-cone, in its normal condition, very frequently possesses 

 ' inverted cones,' i. e. cones with their apices pointing upwards, as AA, 

 as distinguished from what may be called ' ordinary ' cone-in-cone, 

 wherein the points of the cones face downwards, as VV ; (2) to show 

 that Mr. John Young's explanation of the formation of both the 

 ordinary and the inverted cones is probably erroneous, 1 because 

 it altogether fails to account for the phenomena observed ; and 

 (3) to describe certain forms and inner structures of the rock, not 

 hitherto published ; concluding with a few suggestions regarding 

 the probable origin and mode of formation of the conic masses. 



1. Inverted Cones. 



Instances of layers of cone-in-cone forming portions of nodules 

 were referred to in 1820, 2 but, so far as I know, no trustworthy 

 illustrations of inverted cones appeared until those given in my own 

 paper in 1887. 3 Now, these ' finds ' seem to afford sufficient evidence 

 to prove that Mr. Young's theory of cone-formation must be rejected, 

 provided (as it is natural and reasonable to suppose) that true cone- 

 in-cone can be produced in one way alone. But Mr. Young, having 

 come to the conclusion that the Scottish cone-in-cone, from which 

 he obtained his specimens and constructed his theory, was a forma- 

 tion resulting from the ebullition of gases passing upwards through 

 a plastic sediment during deposition in local areas, altogether 

 repudiated the idea of true conic layers having the bases of the 

 cones facing downwards. He endeavoured to account for the 

 existence of nodules upon whose upper surfaces cone-in-cone 

 occurred with the points in the direction of centre of the mass, and 

 upon whose under surfaces similar structures existed with their 

 apices facing in the same direction, by employing the phenomenon of 

 contraction. This he conceived had acted so powerfully on these 

 cone-in-cone-concretions as to cause them to curl up, hedgehog-like, 

 to such an extent that the conic layer on the top was stretched 

 and even carried round to, and presumably welded together upon, 

 the under side. The very aspect and structure of the nodules that 

 I had studied prevented me from accepting, even for a moment, 



1 Trans. Geol. Soc. Glasgow, vol. viii. (1885) p. 1. 



2 Trans. Geol. Soc. ser. 1, vol. v. pt. 2, p. 375. 



3 ' Notes on Cone-in-cone Structure,' Geol. Mag. p. 17. 



