TRENTON CONGLOMERATE OF RYSEDORPH HILL 107 



to indicate that this genus had its center of development farther 

 east, either in the Atlantic or in northern Europe. 1 



ORIGIN OF THE CONGLOMERATE 



The origin and composition of the conglomerate bed, whose 

 fauna has here been investigated, invites some farther remarks. 

 The becl is composed of pebbles of lower Cambric, Chazy, Beek- 

 mantown and lower Trenton age. The explanation of this re- 

 markable accumulation is largely to be found through an inquiry 

 into the direction whence these pebbles came. 



The extremely rare lower Cambric pebbles are identical with 

 those of the lower Cambric conglomerate exposed at Troy and 

 Schodack Landing. They may therefore be derived either from 

 that conglomerate bed or from the mother bed of that conglom- 

 erate. They can not be derived from the west or northwest, as no 

 lower Cambric beds are known in those directions, while they 

 are known in the regions to the north and east. Neither is the 

 Chazy known farther west, nor in the Mohawk region; it extends 

 largely to the north in the Champlain region and is quite cer- 

 tainly present in the limestones of the Taconic region. The 

 Lowville limestone and gray lower Trenton limestone pebbles 

 may be derived from the west. It is not to be assumed that the 

 materials of the conglomerate were gathered from different or 

 even opposite directions; and, as the lower Trenton is also well 

 exposed to the north and south, and is supposed to form a part 

 of the metamorphic rocks in the Taconic region to the east, it is 

 more than probable that these were derived from the east or 

 north rather than from the west. Finally the black Trenton lime- 



i The forms cited here constitute an element in the Trenton fauna of eastern America which is 

 evidently more fully represented in the homotaxial beds of northern Europe. As the latter, and 

 specially the European northwest, was at that time a part of the Atlantic basin, the presence of 

 these forms must be taken to indicate some connection of the continental Trenton sea with the 

 Atlantic in the northeast. 



If the " Gronlandischer continent", supposed by Prof. Freeh to have extended in lower Siluric 

 time across the present, northern Atlantic from Baffin Land and Labrador to Scotland and Scandi- 

 navia, was a reality, its southern coast would have furnished either the center of development or 

 the highway for the migrations of these forms and many others, asAsaphus gigas, Calym- 

 mene senaria,Plectambonites sericeus, Platystrophia biforata,Dalmanella 

 testudinaria, Or this tricenaria. Leptaena rhomboidalis, which appear in lower 

 Siluric time on both sides of the Atlantic. 



