340 H. S. WILLIAMS — SILURIAN-DEVONIAN BOUNDJLEY 



was biologically coincident with the physical raising of the eastern 

 border of the continent, an elevation which for the Acadian provinces 

 shut out marine conditions permanently, and made dry land after the 

 Coal Measures had heen accumulated. 



This series of geological events corresponds closely with the events 

 recorded on the British isles, expressed by the estuary conditions of the 

 Old Red, terminating in the Coal Measures, and the final protrusion of 

 land permanently above marine surface. The evolutional changes in 

 the invertebrate organisms, on passing from the Ludlow into theGedin- 

 nian and Coblenzian faunas of western Europe, are also closely paral- 

 leled by the evolution taking place in America at this same stage of 

 events on passing from Lower Helderberg to Oriskany. 



In America the evidence is clear that the Oriskany fauna was not 

 evolved immediately subsequent to the Waterlime stage, although the 

 Oriskany sandstone immediately follows the Waterlime fauna at Spring- 

 port, New York. We know that here the Lower and Upper Pen tarn eras 

 and Delthyris shaly faunas are older than the Oriskany. and also that 

 they are older than the beginning of those physical conditions which 

 mark the great mass of sediments of the Gaspe sandstone. 



In Europe it is believed that the Hercyn and Erbray limestones are 

 equivalent to the arenaceous Coblenzian and Gedinnian of western 

 Europe, but it is not perfectly clear what stratigraphical relation exists 

 between the Konieprussian and the arenaceous faunas further west. 

 The doubtful interpretation of the European equivalency should not be 

 allowed to controvert the positive evidence we possess in America as to 

 the place in the time scale at which the transition took place there. 



TRANSITION FROM MARINE SILURIAN TO OLD RED SANDSTONE IN WALES SYN- 

 CHRONOUS WITH APPEARANCE OF ORISKANY FA UNA IN EASTERN AMERICA 



The above evidence points to the conclusion that the appearance of 

 the marine Oriskany fauna among the formations in eastern America 

 marks the exact stage in the geological history which across the Atlan- 

 tic, in western Europe, is represented by the transition from Silurian to 

 Old Red in Wales, and farther south by the modification of marine 

 faunas from those of the Ludlow into the first arenaceous faunas of the 

 Gedinnian and Coblenzian of western Europe. In regions where these 

 physical conditions did not prevail, a marine fauna of the lower type 

 undoubtedly continued on with less modification, and it is not the 

 continuing of species characteristic of the Silurian into the Devonian 

 which can gainsay the correlation based on positive evolution of new 

 faunas. Where the limestone sedimentation continued unbroken, as in 

 Bohemia, it may be diflicult to determine the exact place in the series 



