XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 389 



after, in the copy of Sedgwick's map published in 1844 by the 

 Geological Society), devised for these rocks the name of the 

 Taconic system, as synonymous with the Lower (and Middle) 

 Cambrian of Sedgwick. These conclusions were set forth by 

 him in 1842, in his report on the Geology of the Northern 

 District of New York (page 162). See farther his Agriculture 

 of New York (I. 49), the fifth chapter of which, " On the 

 Taconic System," was also published separately in 1844 ; when 

 the presence of distinctive organic remains in the rocks of 

 this series was first announced. 



Meanwhile to Professor Hall, after the completion of the 

 survey, had been committed the task of studying and describ- 

 ing the organic remains of the State, and in 1847 appeared 

 the first volume of his great work on the Palaeontology of New 

 York. Since 1842 he had been enabled to examine more 

 fully the organic remains of the lower rocks of the New York 

 system, and to compare them with those of the Old World ; 

 and in the Introduction to the volume just mentioned (page 

 xix) he announced the important conclusion that the New York 

 system itself contained an older fauna than the Upper Cam- 

 brian of Sedgwick. According to Hall, the organic forms of 

 the Calciferous and Chazy formations had not yet been found 

 in Europe, and our comparison with European fossiliferous 

 rocks must commence with the Trenton group. He however 

 excepted the Potsdam sandstone, which already, in 1842, he 

 had conceived to be below the Upper Cambrian of Sedgwick, 

 and now regarded as the probable equivalent of the Obolus 

 or Ungulite grit of St. Petersburg. Thus Emmons, in 1842, 

 asserted, on lithological and stratigraphical grounds, the exist- 

 ence, beneath the base of the New York system, of a lower 

 and unconformable series of rocks, in which, in 1844, he an- 

 nounced the discovery of a distinctive fauna. Hall, on his 

 part, asserted in 1842, and more fully in 1847, that the New 

 York system itself held an older fauna than that hitherto 

 known in the British rocks. 



It is not necessary to recall in this place the details of the 

 long and unfortunate Taconic controversy, which I have re- 



