BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 11, pp. 333-346 May 21 , 1900 



SILURIAN-DEVONIAN BOUNDARY IN NORTH AMERICA. 



BY HENRY S. WILLIAMS 



(Read before the Society December- 28, 1899) 



CONTENTS 



Page 



Questions involved in determining geological boundary planes 333 



The questions defined 333 



Top of the standard Silurian system, the " Tilestones " (= Downton sand- 

 stone) of Wales .334 



Base of the typical Devonian system not known , 334 



Oriskany fauna of America equivalent to lowest arenaceous Devonian 



fauna of Europe 336 



Hercynian faunas Eodevonian 337 



Is the Lower Helderberg equivalent to the Hercynian ? 337 



The real problems in determining the Silurian-Devonian boundary for America. 337 



Character of the evidence as to transition 337 



Merostomes and fishes 338 



Salt basins of Waterlime and Onondaga of the interior and their absence 



in Maine and New Brunswick sections , 338 



Introduction of Oriskany fauna coincident with elevation of present 



Atlantic border of continent 339 



Transition from marine Silurian to Old Red sandstone in Wales synchro- 

 nous with appearance of Oriskany fauna in eastern America * 340 



Summary of geological and stratigraphical argument 341 



The paleontological argument 341 



Nature of the evidence 341 



The Tilestone fauna recognized in the Upper Arisaig by J. W. Salter 342 



Fifteen Lower Helderberg species recognized in Arisaig section by Doctor 



Ami , . . 344 



Place of Tilestone fauna in Arisaig section equivalent to transition from 

 marine to estuary conditions in Gaspe section, and to first appearance 



of Oriskany in Maine and New Brunswick 345 



Summary and conclusions 346 



Questions Involved in Determining Geological Boundary Planes 



THE QUESTIONS DEFINED 



In the determination of the boundary plane for the rocks of a geological 

 province between two great systems, such as the Silurian and Devonian, 

 there are two distinct questions involved : 



XLVIII— Bull. Geol. Soc. Am., Vol. 11, 1899 (333) 



