SIGNIFICANCE OF WIDE DISTRIBUTION OF GRAPTOLITES 237 



gion, according to evidence found by the writer, in the prevailing direc- 

 tion of fossils in the Mohawk region. A few of our Utica forms, as 

 Diplograptus quadrimucronatus, Dicranograptus nicholsoni, again have 

 reached the Pacific basin, but not by way of a North American epiconti- 

 nental sea. 



The absence of typical graptolite shales in the Frankfort and Lorraine 

 suggest that then the arms of the sea that spread over the continent, at 

 this time from the south, were ending blind toward the northeast. 



The Siluric, aside from small occurrences on our northeastern Atlantic 

 border, has furnished only two occurrences of graptolites in the William- 

 son shale of the Clinton and a later one in the Niagaran of eastern Mis- 

 souri. Since only the Upper Siluric graptolite faunas of the Atlantic 

 basin are as yet known, no evidence as to the possible relationship of 

 these faunules to other than the Atlantic basin is at hand. 



In conclusion, I wish to emphasize the fact that inasmuch as the 

 graptolites as planktonic organisms were able to cross the oceans and seas 

 directly instead of creeping along the shores, as the littoral benthonic 

 faunas did, they must not only have wandered infinitely faster and far- 

 ther, but may even have gone in opposite directions to the coexistent 

 littoral faunas. While the appearance of the latter proves the establish- 

 ment of a bridge or littoral highway, that of the former often indicates 

 the opening of an oceanic highway with currents as carriers for the 

 graptolite fauna. And while the former, as a rule, are separated by the 

 deep sea, the latter are connected by it. 



