GRAPTOLITES OF NEW YORK, PART 2 43 



Hudson and bending southeast with the whole belt of " Hudson River shale " 

 north of the Highlands, its last outcrop being observed close to the New- 

 Jersey boundary. It probably continues in the Appalachian trough into 

 Pennsylvania and Virginia. The other branch skirts the Adirondack^ in 

 the Mohawk valley and on their west side, disappearing beneath Lake 

 Ontario to reappear in the Province of Ontario, crossing the same to Col- 

 lingwood, "where it disappears beneath the waters of the Georgian bay 

 and continuing north and west strikes numerous points, capes and islands 

 about the great Manitoulin island dying out to the west and overlaid by 

 newer and overlying formations." 



The reappearance of Utica shale in the center of the Cincinnati geanti- 

 cline at Cincinnati, and its tracing through Ohio (by well borings) demon- 

 strate that the narrow belt of outcrops above delineated, does by no means 

 indicate the whole distribution of this widely extended shale formation. 

 The St John and Ottawa outliers show that the shale extended far on the 

 " Canadian shield " and an outlier at Wells in the southern Adironclacks 

 demonstrates that the Utica sea also swept at least a part of that plateau. 

 The facts of this wide overlap combined with the shaly nature of the 

 rocks and their greatly varying, often considerable thickness indicate that 

 the Utica formation is the result of a great transgression of the sea 

 brought about by a general depression of the northeastern part of North 

 America. The transgressing sea came in from the northeast and brought 

 with it a fauna with decided Atlantic elements ; and currents developed 

 which assisted in spreading the shales and the immigrating fauna far into 

 the epicontinental sea. 1 



The facts of this transgression and enlargement of the northeastern 

 communication with the Atlantic would seem to aid in explaining the 

 differences between the graptolite faunas of the Utica shale and the under- 

 lying beds, and certain peculiarities in the areal distribution of some of the 

 Utica shale graptolites as Corynoides curtus, G 1 o ss ograp t u s 



1 See Matthew, Roy. Soc. Can. Trans. 10 : 15; Ruedemann, Amer. Geol. 1897. 19: 

 367-91 ; 21 : 75-81 ; Ulrich & Schuchert, N. Y. State Mus. Bui. 52. 1902. p. 642. 



