HUDSON RIVER BEDS NEAR ALBANY 56^ 



to Europe was already opened in the younger Trenton per- 

 iod ; f or I s o t e 1 u s g i g a s and Trinucleus concen- 

 tric u s (=0 r n a t u s Stbg.) appear already in the Oaradoc and 

 its equivalents. Triarthrus becki, the most characteris- 

 tic form of the Utica shale^ seems to occur already in the Chas- 

 mops limestone of Sweden. In the later Utica age the Lorraine 

 fauna from the w^estern part of the state seemed to gain the 

 ascendancy, as indicated by the fauna discovered by Beecher near 

 the old Dudley observatory at Albany and by the writer on Green 

 Island. 



The Lorraine fauna, with its close relationship to the Trenton 

 fauna in identical or vicarious forms (a relationship which be- 

 comes still more emphasized toward the interior of the continent 

 in the overlying Kichmond beds) is again evidently an epicontin- 

 ental fauna derived from the Trenton fauna. 



To state it more concisely, the writer believes that the Trenton 

 fauna and its derivative, the Lorraine fauna, are of epicontinental 

 origin, and entered the Hudson valley region from the west, while 

 the Dicellograptus fauna and its derivative, the Utica fauna, are 

 foreign to the continent, and entered it from the Atlantic ocean 

 by way of the Canadian basin. This follows from the necessary 

 assumption of the presence of a Paleo-Appalachian continent 

 {sec Freeh, 54) to the east of North America. The former assump- 

 tion seems to be supported by the indications of the presence of a 

 ne — sw current in the Mohawk region during the Utica epoch, 

 found by the writer in the prevailing arrangement of the grap- 

 tolites, cephalopod shells, sponge spicules, etc. in the shales (55). 

 Lapworth, followed by Walther, maintains (53) that the grapto- 

 lites were planktonic or rather pseudo-planktonic animals which, 

 drifting along the coasts, left their remains in the quieter waters 

 at a certain distance from the coast. This view would also sug- 

 gest that the Trenton and Utica shales were formed along the 

 continental shelf under the influence of currents entering from 

 northeast. The alternations of coarse, mostly barren sandstones 

 VNith fine grained, muddy graptolite-bearing deposits indicate the 

 changing conditions along this coast shelf, which, on the whole, 



