EIvISHA MITCHELL SCIENTIFIC SOCIETY. 61 



the method of reproduction as described above (p. 52) 

 mi^i^-ht have seemed to him more sugg-estive of the coral 

 than of any known form, orofanic or inorg-anic, yet the 

 proof is not positive and I can find no just ground for 

 his position. ^ 



Admitting the organic origin of pala^otrochis, how 

 could it have been preserved? Considering its distri- 

 bution through the rock mass and the position assumed 

 by the individuals, with the material in which they are 

 imbedded, the explanation is possible by different meth- 

 ods. The first that occurs to me, and which is offered 

 merely as a suggestion is this: The indviduals dropped 

 to the sea floor and w^ere imbedded in ooze. This ooze 

 being largely calcareous but containing a considerable 

 amount of silica on beginning to solidify would have 

 formed in it, silicious concretions, just as the\^ are 

 found in the chalk beds of Kngland. Their origin is 

 explained as follows by IveConte: "Nodular concre- 

 tions seem to occur whenever any substance is diffused 

 in small quantities through a mass of entirely different 

 miiterial. Flint nodules in chalk. Carbonate of lime 

 modules in sandstone, &c."^ 



As concretions start around nuclei which are gen- 

 erally of a different material from the concreting sub- 

 stance, and are particularly favored by deca3^ing or- 

 ganic matter, it is quite natural to expect these bodies 

 of organic matter to be encased with silica at the same 



1. I have found several specimens that answer to Professor Em- 

 mons's description of the process by which they are reproduced, and 

 at apparently different stag-es of the process. One of the best, 

 which was not in Enimons's collection, I have shown in Fig-. 15, 

 This answers better to his description than his own fig-ures, 2 

 and 4. 



