GEOLOGY. 279 



lidcs. He considered all the species to be distinct from any that had 

 been found in American rocks of undoubted Silurian age. The 

 pre-silurian age of the formation has also been maintained by him in 

 several more recent publications, such as his American Geology, the 

 several reports on the geological survey of North Carolina, and in his 

 Manual of Geology. 



" On the other hand, Professor Hall placed the whole region in the 

 Hudson River group. In the first volume of the Palaeontology of 

 New York he identifies Atops trilineatus with Triarthrus Beckii, the 

 characteristic trilobite of the Utica slate ; Elliptocephala asaplioides 

 he refers to the genus Olenus, and describes as congeneric therewith 

 another trilobite (0. undulostriatus), said to be from the true Hudson 

 River shales. It is scarcely necessary to state that these identifica- 

 tions have always afforded an extremely powerful objection against 

 the correctness of the position assumed by Emmons, because no spe- 

 cies of trilobite is known to range from the Primordial Zone up to 

 the top of the Lower Silurian. Hall's first volume was published in 

 1847, and as it is unquestionably the most important work on the 

 Lower Silurian Fossils of North America, it has been generally ac- 

 cepted by our physical geologists as a guide. It is not surprising 

 therefore that, in all the discussions that have taken place during the 

 last fourteen years upon the age of these rocks, the majority of those 

 who did not profess to be naturalists should have arranged them- 

 selves on the side of the leading palaeontologist of the country. 



" The formation was traced from New York through Vermont, and 

 there identified, by Professor Adams, the State Geologist, with the 

 Hudson River group. The Canadian surveyors continued it with 

 great labor through a mountainous and partially uninhabited country 

 for nearly five hundred miles further, from the northern extremity 

 of Vermont to the neighborhood of Quebec, and thence along the 

 side of the St. Lawrence to the mouth of that river at Cape Gaspe. 

 In Canada the nomenclature of the New York Survey was adopted 

 for all the formations, and it appears 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 par- 

 ticular series of rock. It has therefore always been called the Hud- 

 son River group in the publications of the Canadian Survey." 



Within a comparatively recent period, however, Sir William Lo- 

 gan and the Canadian geologists have found in the rocks in the vi- 

 cinity of Quebec, heretofore referred by them, in opposition to the 

 views of Dr. Emmons, to the age of the Hudson group, a large num- 

 ber of fossils which prove unquestionably that the Quebec rocks are 

 at least as ancient as the strata acknowledged to form the base of the 

 Silurian System, or the " Potsdam sandstone," and as, in Vermont, 

 strata, regarded of the same age as the Quebec rocks, appear to 

 be subordinate to the Potsdam sandstone, it follows the position con- 

 tended for by Dr. Emmons is probably true. 



If the views of Dr. Emmons are to be accepted as entirely in con- 

 formity with the real truth, it would seem as if the name " Taconic 

 System," given by him to the lowest group of stratified rocks, ought 

 to' supplant the names "Huronian" and "Laurentian" adopted by 

 the Canadian geologists ; the former being considered as the " Upper 



