ElvISHA MITCHELL SCIENTIFIC SOCIETY. ^ 68 



of Paleotrochis, as some of them presented to the Yale 

 cabinet by Prof. Dana, were sent to him by Prof. Em- 

 mons, and the rest were g-iven to the writer by Prof. 

 W. C. Kerr, the present state g-eolog-ist of North Caro- 

 lina. * * * * Admitting- the inorg-anic nature of 

 these remarkable forms, their orig-in becomes an interest- 

 ing- question, and it certainly is not easy to g-ive a satis- 

 factory explanation of it. They appear, however, to have 

 some analog-y with "cone in cone," which, as the writer 

 has shown elsewhere,' is probably due to the action of 

 pressure on concretionary structure when forming-. In 

 some respects the two are quite distinct, but evidence of 

 pressure is clearly to be seen in both." 



Kerr evidently ag-reed with Marsh as to the inorg-anic 

 nature of the Paleotrochis, and Mr. C. D. Walcott, the 

 director of the U. S. Geolog-ical Survey, entertains the 

 same opinion."^ 



According- to both Emmons' and Kerr's descriptions, 

 these peculiar forms appear to occur in what are now 

 known to be the acid effusive rocks. In his descriptive 

 section of the rocks which carry the Paleotrochis, Em- 

 mons names the following (p. 56): 



"Granular quartz, sometimes vitreous and filled with 

 fossils and siliceous concretions of the size of almonds. 



"Slaty quartzite with very few fossils. 



"Slate without fossils. 



"White quartz more or less vitrified filled with fossils 

 and concretions. 



"Jointed gfranular quartz with only a few fossils." 



And he says: "These fossils also occur in the variety 

 of quartz or quartzite, which I have described as burrh- 

 stone, and which is often porphyrized." (p. 56.) 



An interesting- point is suggested in the above succes- 

 sion of rocks, namely, that there was more than one vol- 



Proc. Amer. Assoc. Adv. Sci., vol. 16, 1867, p. 135, 

 Private cominunication to the writer. 



