58 JOURNAL OF THE 



are composed, show that there was no pressure when 

 forming-, (p. 56, also Ficr.l4.) Neither are they in 

 the slig-htest deg^ree similar in form. 



" Undoubtedly few of the structures classed under 

 the general head of concretions are more curious than 

 cone-in-cone. The name is descriptive, the structure 

 consisting' of corrug^ated or crenulated conical layers, 

 one within another, and in the more complex specimens 

 it is seen that thin layers of the rock, a calcareous and 

 sideritic clay, is composed of the closel}^ crowded nests 

 of cones, the axes of the cones being* transverse to the 

 bedding' planes. The height of the cones measures the 

 thickness of the layers, which is commonly one to four 

 inches. It seems necessary to suppose that during- the 

 compression of the layers of clay by vertical pressure 

 it is divided by an indefinite series of conical g'liding- 

 surfaces, which are corrug-ated b}^ the intermittent 

 character of the movement. "^ 



"Clay iron stones sometimes exhibit the reg-ular 

 structure known as cone-in-cone, in which case the 

 seam has a tendency to divide into cones, the bases of 

 which are towards the top and bottom of the bed, while 

 their apices are directed towards the center. "~ 



By comparing; the character and mode of occurrence 

 of pala}otrochis with cone-in-cone, it is seen that there 

 is no similarity between them, but the quotations are 

 g-iven in full to show that no inorg-anic form has yet 

 been described which explains the orig-in of pala^otro- 

 chis. 



The palaiotrochis is not two cones applied base to 

 base, that simply roughly suggests the general form, 

 and its failure to conform, even approximately, to a 



1. Dynamical and Structural Geol., W. O. Crosby, p. 278. 



2. Ore deposits, J. A. Philips, p. 165. 



