108 Barrandet Logan and Hall 



of that river at Cape Gaspe. In Canada the nomenclature of the 

 New York Survey was adopted for all the formations, and it ap- 

 pears from his several reports that Sir W. E. Logan could find 

 nothing in the physical structure of the country to authorize him 

 to make an exception in favor of this particular series of rocks. 

 It has therefore always been called the Hudson River group in 

 the publications of the Canadian Survey. 



It will be seen by the following correspondence that the new 

 light thrown upon the question of the age of these rocks by the 

 fortunate discovery of a large number of fossils near Quebec, now 

 leads Sir William to place them at the base of the Lower Silurian, 

 and as he states that the shales in Vermont, in which the trilobites 

 noticed in Mr. Barrande's letter to Prof. Bronn have been found, 

 may be subordinate to the Potsdam, it seems probable that the 

 sequence contended for by Emmons will turn out to be at least 

 for the greater part the true one. 



II. 



On the Primordial Fauna and the Taconic System of Emmons, 



IN A LETTER TO PrOF. BrONN OF HeIDELBERG.* 



"Paris, July 16, 1860. 



" I have recently received, thanks to the kindness of 



Mr. E. Billings, the learned palaeontologist of the Geological Sur- 

 vey of Canada, a very interesting pamphlet entitled ' Twelfth An- 

 nual Report of the Regents of the University of the State of New 

 York, 1859.' If you possess this publication, you will find there, 

 at page 59, a memoir of Prof. J. Hall, entitled * Trilobites of the 

 shales of the Hudson River group.' This savant there describes 

 three species under the names Olenus Thompsoni^ Olenus Ver- 

 montana, and Peltura ( Olenus) holopyga. The well-defined cha- 

 racters of these trilobites are described with the clearness and 

 precision to be expected from so skilful and experienced a pal- 

 aeontologist as James Hall. 



" Although the specimens are incomplete, their primordial na- 

 ture cannot admit of the least doubt, when the descriptions are 

 read, accompanied with wood engravings, which the large dimen- 

 sions of these three species render suflBciently exact. The first is 

 105 millim. long by 80 broad, the other two are somewhat 

 smaller. 



* Proceed, Boston S. N. Hist., Vol. vii, Dec. 1860, p. 371. 



