OSCILLATORY CHARACTER OF CONTINENTAL SEAS 365 



adapted to pelagic conditions. Indeed, the suggestion of currents locally 

 prohibiting deposition is a welcome addition to the evidence on which 

 these long channels or straits are inferred, since it affords a satisfactory 

 explanation of the absence of graptolite-bearing shales in the areas that 

 the channels had to cross in order to connect with the oceanic basins. 



An adequate discussion of these channels and their relations to marine 

 currents can not be undertaken here. It must suffice to say that the 

 faunal evidence, which is abundant and requires an opening at either 

 end, as well as continuous currents to transport the floating organisms, 

 is in accord with the structural and stratigraphic phases of the problem. 

 In such channels, therefore, currents capable of affecting the character 

 and amount of deposits are not only admitted but averred. Neither 

 have I any desire to question the effect of currents on the distribution 

 of marine organisms. Indeed, I am convinced that in the oceanic waters 

 themselves the distributing agent of paramount importance is found in 

 the currents. (See also page 517.) 



Current scour improbable in interior continental seas. — The case with 

 respect to the broad inland seas is altogether different. Willis admits 

 that currents competent to do the work in these inland basins are possible 

 only under the supposition that channels, extending, in the case of North 

 America, from the Gulf of Mexico completely across the continent to 

 the Pacific and Arctic oceans, were opened at times of great marine 

 transgressions. If they occurred at all, they must be exceedingly rare 

 and perhaps in no case positively demonstrable. Sufficiently wide trans- 

 gressions ai^e indicated in most published paleogeographic maps, even 

 in many of those recently issued in the bulletin of the Geological Society 

 of America by Schuchert. But most of these maps are synthetic in that 

 they cover two or more, often very different, stages of the shoreline. 

 The more detailed our stratigraphic studies the more we are obliged 

 to confine the continental seas to definitely limited basins. These con- 

 tinental 1)asins are in communication with one or another of the oceanic 

 basins, but the oceans themselves are only at rare times in communication 

 by means of these interior basins. As to the invasions from the Gulf 

 of Mexico, I doubt if these at any time mingled freely with waters 

 coming in from either the Pacific or the Arctic sides^^. 



The evidence on which great marine transgressions are postulated is, 

 at least in its essential features, purely faunal. This evidence, moreover, 

 usually rests on so-called cosmopolitan faunas. Indeed, the reputed 



*The Invasion diagrams shown on pages .'^46 and .147. being founded on synthetic 

 paleogeographic maps, are necessarily, and for the same reasons, at variance with this 

 opinion. 



