Vol. 50.] ' DEVONIAN ' SEEIES IN PENNSYLVANIA. 737 



(7) The phenomena of the corrugated and wrinkled surfaces, both 



upon the sides and the bases of the cones, the dark clayey 

 lateral ridges or rings encircling the cones, and the serrations 

 upon the bases of the cone-layers, all appear to indicate unmis- 

 takably the operation of lateral radial contraction, squeeze, or 

 pressure acting towards the centre of the formations. 



(8) Further, an inspection of the minute texture of the walls of the 



cones reveals a semi-crystalline structure, — namely, innumerable 

 aggregates of miniature or semi-microscopic cone-in-cone com- 

 parable with the main structure. 



(9) Thus the conclusion is reached that cone-in-cone must be regarded 



as a species of concretion, whose peculiar mineral and chemical 

 composition induced such pressure among the particles while 

 undergoing transformation as to produce the forms of cones 

 and (by differentiation) parts of cones all through the separate 

 layers, collectively and yet independently. 



In other words, this cone-in-cone is a final product of the 

 concentration of calcium carbonate around certain nucleal 

 points within, or horizontal planes of original stratification of, 

 detrital sedimentary fossiliferous rocks ; which accretionary 

 process involved the partial expulsion of the non-crystallizing 

 contained clayey material, and this material, seeking or 

 struggling, in obedience to the laws of crystallization, to 

 escape, was perforce (owing to close confinement all around, 

 with ever-increasing contractile inward and radial y)ressure 

 tending to keep it back) compelled to assume the form of 

 horizontal rings or ridges : and these were the weakest places 

 which the pressure-produced conic cleavage afforded. The cal- 

 careous semi-crystalline fabric of cones having completed its 

 mutations or gone through the requisite evolutions, with the 

 argillaceous rings of squeeze brought into equilibrium with 

 the rest of the structure, cone-in-cone was complete. 



Finally, the observed structures in the typical Portage cone^ 

 in-cone agreeing, as they do, closely in every essential particular 

 with the cone-in-cone of the Coal Measures in Great Britain 

 and in North America, impel the present writer to regard the 

 origin and formation of one and all as practically identical in 

 original composition — chemically and physically, 1 and, in the 

 main, to accept the conclusions of other observers in this con- 

 nexion, who consider the formation to be a result of pressure 

 acting upon concretions. 



1 Many examples of cone-in-cone, as they exist to-day, are unquestionably 

 what may be called re-altered products — that is, ' tertiary ' formations ; for the 

 author's collection contains cone-in-cone composed of haematite, limonite, fer- 

 riferous quartzite, quartzite, pyrites or marcasite, and a variety of more or less 

 iron-impregnated siliceous rocks. 



