268 GEOGNOSY OF THE APPALACHIANS. [XIII. 



Cambrian, as defined by Sedgwick, is represented in North 

 America by the upper portion of the Champlain division of 

 New York, from the top of the Chazy, while the Middle and 

 Lower Cambrian have their equivalents in the Quebec group, 

 the Chazy, Calciferous, and Potsdam, and in the strata holding 

 Paradoxides and other primordial forms in Massachusetts, New 

 Brunswick, and Newfoundland. The precise relation of these 

 to the Potsdam formation of New York is yet to be deter- 

 mined, as well as the question whether there exists in the 

 Appalachians any palaeozoic rocks belonging to a lower horizon 

 than the Potsdam. For a further discussion of these questions 

 the reader is referred to Essay XV. in the present volume.] 



In May, 1861, I called attention to the fact that beds of 

 quartzose conglomerate at the base of the Potsdam in Hem- 

 mingford, near the outlet of Lake Champlain, on its western 

 side, contain fragments of green and black slates, " showing the 

 existence of argillaceous slates before the deposition of the 

 Potsdam sandstone." * The more ancient strata, which fur- 

 nished these slaty fragments to the Potsdam conglomerate, 

 have perhaps been destroyed, or are concealed, but they or 

 their equivalents may yet be discovered in some part of the 

 great Appalachian region. They should not, however, be 

 called Taconic, but receive the prior designation of Cambrian, 

 unless, indeed, it shall appear that the source of these slate 

 fragments was the more argillaceous beds of the still older 

 Huronian schists. Emmons regarded his Taconic system as 

 the equivalent of the Lower (and Middle) Cambrian of Sedg- 

 wick ; but when, in 1842, Murchison announced that the name 

 of Cambrian had ceased to have any zoological signili' 

 being identical with Lower Silurian, t Emmons, conceiving, as 

 he tells us, that all Cambrian rocks were not Silurian, instead 

 of maintaining Sedgwick's name which, with the progress of 

 paleontological study, is assuming a great zoological importance, 

 devised the name of Taconic, as synonymous with the Lower 

 (and Middle) Cambrian of Sedgwick. t 



* American Journal of Science (2), XXXI. 404. 



t Proc. Geol. Soc. London, III. 642. 



Emmons, Geol. N. District of New York, 162 ; and Agric. of New York, 

 I. 49. 



