326 GEOGNOSY OF THE APPALACHIANS. [XIII. 



the forms of a foraminiferal organism, the Eozoon Canadense of 

 Dawson. This singular supplement to the hypothesis of epigenic 

 change recalls the notion of the older naturalists, who, rather than 

 admit the organic origin of shells found in the rocks, imagined 

 them to have been generated by a plastic force. It is evident that 

 it makes little difference what mineral species is taken as a starting- 

 point for these transformations, and Dr. Genth has assumed corun- 

 dum. In a recent paper (Proceedings of the American Philosophi- 

 cal Society, September 19, 1873) he has discussed various facts 

 observed in the association and envelopment of the minerals associ- 

 ated with it, and concludes that there have been formed from corun- 

 dum, by epigenesis, spinel, tourmaline, fibrolite, cyanite, paragonite, 

 damourite and other micas, chlorite, and probably various feld- 

 spars. According to him, great beds of micaceous and chloritic 

 schists have resulted from the transformation of corundum, and 

 even the beds of bauxite, a mixture of hydrous aluminic and ferric 

 oxides, allied to limonite, which abounds in certain tertiary depos- 

 its, were once corundum or emery, from which this amorphous 

 hydrate is supposed to have been derived by a retrograde metamor- 

 phosis ; a striking example of the strange conclusions to which this 

 doctrine of epigenic pseudomorphism may lead. The corundum- 

 bearing vein-stones present close resemblance in the grouping and 

 association of minerals to the granitic and calcareous vein-stones 

 described in Essay XI. of the present volume. See, further, the 

 author's criticisms on this subject, Proceedings Boston Society of 

 Natural History, March 4, 1874.] 



Coming now to his criticism of the first part of my address, with 

 regard to New England rocks, Professor Dana asserts that " there 

 are gneisses, mica-schists, and chloritic and talcoid schists in the 

 Taconic series." I have, however, shown in my address that Em- 

 mons, the author of the Taconic system, expressly excluded there- 

 from the crystalline rocks, which he included in an older primary 

 system ; excepting, however, certain micaceous and talcose beds, 

 which he declared to be recomposed rocks, made up from the ruins 

 of the primary schists, and distinguished from these by the absence 

 of the characteristic crystalline minerals which belong to the Green 

 Mountain primary schists. 



Again, Professor Dana states that I make the crystalline schists 

 of the White Mountains a newer series than the Green Mountain 

 rocks. Such a view of their geognostical relations has been main- 

 tained for the last generation by the Messrs. Rogers, Logan, and 



