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NEW YORK STATE MUSEUM 



tively which lies higher. The occurrence of still another Clono- 

 graptus, CI. m i 1 e s i Hall, in black shales near Georgia Vt., 

 indicates however that there may be Cambric subzones, charac- 

 terized by forms of Dictyonema and the two species of Clono- 

 graptus. 



These subzones may lead very gradually into the Tetragraptus 

 and Phyllograptus zones of Beekmantown age; for the occur- 

 rence of a C 1 o n o g r a p t u s cf. flexilis Hall (a Point 

 Levis form) between the two Dictyonema horizons reported by 

 Nilsson and Tellander and the finding of a typical specimen of 

 Bryograptus kjerulfi in the Tetragraptus shale of 

 the Deep kill by the writer, as well as some other facts of dis- 

 tribution, would indicate the presence of such transitional zones 

 between the Dictyonema and Tetragraptus beds. These would 

 be equivalent to the Ceratopyge beds of Scandinavia, which 

 there intervene between these graptolite beds, and to the Tre- 

 madoc of Britain. 



Bearing of the occurrence of the Dictyonema bed on Cambric 

 paleogeography 9 



Messrs Ulrich and Sehuchert have undertaken the task of 

 elaborating a theory in explanation of the differences in 

 stratigraphic succession and faunistic aspect of the Appala- 

 chian region and the area to the west of the same during paleo- 

 zoic time 1 . The solution is found in the assumption of the pres- 

 ence of one, or at times, two parallel basins, separated by and 

 inclosed in folds or barriers, and extending during the greater 

 part of the Paleozoic over the territory of the present system 

 of Appalachian folds. This theory not only serves to clarify a 

 multitude of well known stratigraphic and paleontologic facts, 

 but is also an incentive to investigations in further elaboration or 

 modification of its details. 



The facts presented in this paper furnish, on one hand, a new 

 argument for the presence of such basin, and, on the other, 

 appear to necessitate a modification in regard to the fixation of 

 the date at which one of them, the Levis basin, is supposed to 

 have originated. 



1 Paleozoic Seas and Barriers in Eastern North America. N. Y. State Paleon- 

 tologist. An. Rep't. 1901. p. 633-63. 



