236 CONFERENCE ON PALEOZOIC PALEOGEOGRAPHY 



the arrival of some of the forms of this far distant basin by a current 

 from the west. 



'The writer has inclined to the view that this connection with the Pa- 

 cific could have been transcontinental by means of the Beekmantown 

 transgj-ession. Doctor Ulrich, however, has arrived at a different view, 

 "since the continental seas of the required size and location can not be 

 establislied and indeed seem to have been impossible." He states in a 

 lettei- to me his conception as follows: 



"As I see it, the widely distributed graptolite fauua^, lilie the Tetragraptus 

 and Neuiagraptus, attained their great dispersal solely by means of oceanic 

 currents. The channels in whose deposits we now find these faunas were, as 

 you yourself have indicated, thoroughfares for such currents. In the cases 

 of the Levis, Athens, and Ouachita troughs, it seems to me demonstrable that 

 they were channels connecting at both ends with Atlantic oceanic basins and 

 that they passed around the inner sides (and thus separated off from the 

 maiu mass of the continent) certain large marginal islands (Taconia, Ap- 

 palachia, and Llano). As plotted on my maps, the Levis Channel passes up 

 the Saint Lawrence to the east side of the Champlain Valley, and thence 

 south to northern New Jersey, where it joins the Atlantic. The Athens 

 Channel begins on the north at Chesapeake Bay, extends along the eastern 

 side of the Appalachian Valley to central Alabama, beyond which it connects 

 with the Gulf of Mexico. The Ouachita Channel connected with the Gulf 

 through the Mississippi embayment, passed westward through central Arkan- 

 sas and Oklahoma, and thence probably turned southward to open into somo 

 western part of the Gulf. 



"How these graptolites got into the Pacific, or how those of the Pacific 

 got into the Atlantic is a more difficult problem. Possibly the isthmian region 

 was submerged at such times --or it may be that a channel across northwest- 

 ern South America afforded tt e necessary means for communication. We do 

 not know." 



The graptolite fauna of the Kormanskill shale, of approximate Black 

 Eiver age, is distinctly Atlantic in its aspect and is common to north- 

 eastern America and Europe. But some of its elements have also found 

 their way into Arkansar; and British Columbia and into the Pacific basin 

 and Australia. 



The leading species of the graptolite shales corresponding to the Upper 

 Trenton (Magog shale) and of the Utica shale are again common to 

 Europe and eastern North America and are Atlantic forms. In Utica, 

 time an arm of the Atlantic entered from the northeast, or Lower Saint 

 Lawrence region, far on the continental platform, and, as indicated by 

 the graptolite facies, had one or more outlets that completed a circuit 

 back to the Atlantic, the current entering from the Saint Lawrence re- 



