REPORT OF THE STATE PALEONTOLOGIST 1902 957 



We have seen that the Dictyonema fauna is an undoubted 

 Atlantic fauna. In North America it has been recognized in 

 the St John basin of New Brunswick, on Cape Breton island 

 and at several places on the south shore of the St Lawrence 

 from Cape Rosier to Matane river. It has now been found as 

 far south as Rensselaer county in New York and probably ex- 

 tends through the slate belt of New York and Vermont. It is 

 hence, with the exception of the Levis region, where it has not 

 yet been found, about coextensive with the present known ter- 

 ritory of the Phyllograptus fauna. Like the latter, it has not 

 been found either east or west of this long belt and is therefore 

 to be assumed to have entered from the Atlantic, a basin of 

 similar configuration and extension as the Levis channel, in 

 which the Atlantic waters deposited the Phyllograptus fauna. 



The Dictyonema shale is now however of Upper Cambric age, 

 of which it represents the closing period wherever it has been 

 found. It stands, lithologically and faunistically, in the same 

 relation to the upper Potsdam of the Champlain region as the 

 later Phyllograptus shales to either the Beekmantown beds, with 

 w T hich the writer correlated them, or to the Chazy beds, with 

 which they are equivalent according to Ulrich and Schuchert's 

 view T s. The Dictyonema beds represent, like the Phyllograptus 

 shale, the graptolite shale facies of a trilobite-gastropod-bearing 

 limestone (or sandstone in part) which adjoins the slate belt 

 closely to the west and northwest. Ulrich and Schuchert see 

 in the parallelism of the two different faunas and rock, series 

 (Phyllograptus shales and Chazy limestone) proof of the pres- 

 ence of twin channels, the Levis channel and Chazy basin, stat- 

 ing that " the respective faunas and the lithologic character of 

 the deposits in the twin channels are so different that we can 

 not doubt the thorough effectiveness of the Quebec barrier dur- 

 ing the whole of Chazy time." Accepting, for the purpose of 

 further argument, the correctness of the postulation of this bar- 

 rier to explain the stated facts, it follows that a like barrier of 

 equal extent must be postulated for the late Cambric time, and 

 that the beginning of the elevation of this " Quebec " barrier, 

 the northern extension of the "Appalachian valley fold ", must 

 be placed in late Cambric time, instead of at the beginning of 



