THE PLACE OF FAUNA OF ARISAIG SECTION 345 



nian.* Their identification with previously described formations of the 

 eastern provinces is as follows : 



F 3 , Upper Red slate and sandstone = Mispec group. 



F 2 , Middle gray sandstone and slate group =Dadoxylon sandstone and cordaite 



shale. 

 F 1 , Lower conglomerate group = Bloomsbury conglomerate. 



E 6 , Lower Helderberg 



PLACE OF TILESTONE FAUNA IN ARISAIG SECTION EQUIVALENT TO TRAN- 

 SITION FROM MARINE TO ESTUARY CONDITIONS IN GASPE SECTION, AND 

 TO FIRST APPEARANCE OF ORISKANY IN MAINE AND NEW BRUNSWICK 



The paleontological evidence of this Arisaig section appears therefore 

 to be as clear as the general geological evidence in fixing the place of 

 the Silurian-Devonian boundary for the American continent. This evi- 

 dence may be summed up as follows : 



In the Arisaig section, at the point where the marine conditions pass 

 up into non-marine, a transition fauna appeared (D of Honeyman's 

 paper), which was unhesitatingly identified as the equivalent of the top- 

 most fauna of the typical Silurian system of Great Britain by the official 

 paleontologist of that survey, during the lifetime of Murchison, the 

 founder of the Silurian system. 



This fauna appeared after the Lower Helderberg fauna was in the 

 region, as shown by the recognition of at least fifteen Lower Helderberg 

 species in the Upper Arisaig formation by Doctor Ami. 



No marine paleozoic fauna later than the Nictaux, containing some 

 Oriskany species, is recorded for this Nova Scotia region. 



In New Brunswick, in the Gaspe peninsula, the same general sequence 

 is repeated. The Gaspe limestone carries a fauna which has been de- 

 fined as equivalent to the Niagara and (its upper part) Lower Helder- 

 berg. No Tilestone fauna has been identified in these rocks, but the 

 place of transition from the limestones into the following Gaspe sand- 

 stones was recognized long ago by Logan as nearly equivalent to the 

 Oriskany of the New York section. The following sandstones contain 

 almost no marine fossils, but hold plants (Psilophyton, etcetera) of Devo- 

 nian age. The place of termination of the marine faunas is equivalent 

 to the place of the transition in the Arisaig section from upper Arisaig 

 to Devonian; and both correspond as closely as could be wished with 

 the transition from Silurian into Old Red sandstone in southern Wales. 



In Maine I have recently recognized another representative of the 

 Tilestone fauna, in a formation to which I gavef the name of Chapman 



*Loc. cit., p. 49P. 



t Bulletin No. 165, U. S. Geol. Survey. 



