TRENTON CONGLOMERATE OF RYSEDORFH HILL 105 



before or contemporaneously with the lower part of the shale, as 

 indicated by the presence of one of the characteristic graptolites 

 of the shales and the lower Trenton aspect of the entire assem- 

 blage. In this limestone fauna, then, we have a direct means of 

 comparing lower Trenton forms of the eastern border and of the 

 continental sea, living in the same bathymetric zones and under 

 the same marine conditions, and of determining whether the incur- 

 sion of the eastern graptolite fauna into the continental border 

 sea indicates the opening of an entirely new but temporary con- 

 nection with the Atlantic ocean, or whether Atlantic, or rather 

 European connections have had an appreciable influence also on 

 the faunas of the limestone-depositing Trenton sea. The latter 

 suggestion is in a certain measure supported by the appearance 

 of the Normans kill graptolites in the limestone, but, in order 

 to establish the conclusion, it is, in the writer's belief, fully 

 demonstrated by a number of other fossils appearing in the 

 limestone. 



The species on which this conclusion is mainly based are, 

 besides the above mentioned graptolites, whose habitat is the 

 eastern border region and northern Europe: Christiania 

 trentonensis sp. nov., which is well represented in the 

 lower Siluric of Europe, by closely similar species, though in 

 America only known heretofore by a Helderbergian species; 

 the two species of Tretaspis, a genus unrepresented in the 

 American Trenton fauna but widely and richly represented by 

 allied species in the lower Siluric terranes of Great Britain, 

 Bohemia and Scandinavia ; Am pyx ha status, which 

 belongs to a subdivision of that genus (Lonchodo m a s), not 

 represented in the Trenton of North America, but present at this 

 time in northern Europe (A mpyx ro stratus); the species 

 of Remopleurides, which have not been found in the cen- 

 tral continental region; the Sphaerocoryphe, which thus far 

 is definitely known only from this locality, and which also is 

 a foreign element to the Trenton of North America. Remo- 

 pleurides striatulus Walcott, and Sphaerocory- 

 phe robustus Walcott, occur at Trenton Falls only in higher 



