XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 403 



horizon in Europe was then well determined, but, in deference 

 to the conclusions of Adams and of Logan, assigned them to a 

 position at the summit of the Hudson River group ; Hall him- 

 self never having examined the region stratigraphically. (Amer- 

 ican Journal of Science (2), XXXI. 221.) In justification of 

 this position he appended to his description the following note 

 (Ibid., pages 213, 221) : "In addition to the evidence hereto- 

 fore possessed regarding the position of the slates containing 

 the trilobites, I have the testimony of Sir William Logan that 

 the shales of this locality are in the upper part of the Hudson 

 River group, or forming part of a series of strata which he is 

 inclined to rank as a distinct group above the Hudson River 

 proper. It would be quite superfluous for me to add one word 

 in support of the opinion of the most able stratigraphical geol- 

 ogist of the American continent." Paleontology and strati- 

 graphy here came into conflict, and it was not till in 1860, 

 when Mr. Billings, in the face of the evidence adduced from 

 the latter, asserted the primordial age of the Point Levis fauna, 

 that Sir William Logan attempted a new explanation of the 

 stratigraphy of the region; declaring at the same time that, 

 "from the physical structure alone, no person would suspect 

 the break which must exist in the neighborhood of Quebec ; 

 and without the evidence of the fossils every one would be 

 authorized to deny it." (Ibid., page 218.) 



The typical Potsdam sandstone of the New York system, as 

 seen in the Ottawa basin in northern New York and the adja- 

 cent parts of Canada, affords but a very meagre fauna, includ- 

 ing two species of brachiopods, one or two gasteropods, and a 

 single crustacean, Conocephalites (Conocoryphe) minutus, found 

 at Keeseville, New York. In 1852, however, David Dale 

 Owen found and described an extensive fauna in Wisconsin, 

 from rocks which were regarded as the equivalent of the Pots- 

 dam sandstone ; while the observations of Shumard in Texas, 

 in 1861, and the latter ones of Hay den and Meek in the Black 

 Hills, have since still further extended our knowledge of the 

 distribution and the organic remains of the rocks which are 

 supposed to represent, in the west, the Potsdam and Calcifer- 

 ous formations of the New York system. 



