,.>. 



C. D. WALCOTT — THE TERM "HUDSON RIVER GROUP. 



calcareous, and forma the upper pari of the blue limestone of these two 

 states.* 



In January, L842, I>r. Emmons described a series of shales in the Hudson 

 River valley, and spoke of them as the Hudson River Beries or group. He 

 Baysf that the whole extern of this group north and south is not well ascer- 

 tained. It is known, however, to appear far northeast of Quebec, from 

 whence it is traced south through Canada, Vermont and New York, and 

 thence through Pennsylvania into the southern state-. He does not corre- 

 late it with the Lorraine series of the northwestern part of New York. 



Professor dames Hall, in mentioning the Hudson River group in the 

 report of the Fourth district, says : X 



■■ Where the strata are undisturbed a well marked line of division usually separates 

 this group from the Utioa slate; but along the Hudson river, and in other places 

 where disturbance has prevailed, the two are not easily separable." 



A list of fossils characteristic of the group is given, nearly all of which 

 are found in the upper division hut not in the Hudson River valley. 



Professor Hall described the fossils of the Hudson River group in the 

 first volume <>f the Paleontology of New York. L847. The larger propor- 

 tion of the species illustrated, with the exception of the graptolites and a 

 \'r\\ Lower-Cambrian fossils from east of the Hudson, were obtained from the 

 interior of the state of New York, southern Indiana ami Ohio, ami north- 

 ern Wisconsin. At Waterford,on the Hudson, a few species were collected 



that served to connect the fauna of the Frankfort .-hale with that of the 

 Hudson River shale; of this fauna the single species, Ambonychia r<t<li<tt<t, in- 

 dicates the fauna of the upper division of Yanuxciii. The graptolites of 

 tin- black -hale on the west Bide of the Hudson river, as known under the 

 present nomenclature, include the Id genera ami '_!'.» species listed below, 6 

 genera ami !» species of which occur in the Utica shale of the Mohawk 

 valley : 



Rastrites barrandi, I [all. 

 Qraptolithn* (?) In, ,-,'.<, Hall. 

 Leptograptus subtenuis, Hall. 

 Amphigraplus divergent, Hall. 

 Stephanograptus gracilis, Hall. 



surcularis, Hall. 

 DidymograptuB 8erratultis, Hall. 



lagittariw, Hall. 

 ( 1rmatograptu8 multifaseiatus, Hall. 



I oc. 'it . i 



I ! I | : 



\ ■> , Survey Fourth 0e< i ■.. p 30. 



