No. 4.] HUNT — ON CAMBRIAN AND SILURIAN. 431 



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. 

 Jour. Sci. IT, xxxi, 221.] In justification of this position he 

 appended to his description the following note, [Ibid, pages 

 213, 221 :] "In addition to the evidence heretofore possessed 

 regarding the position of the slates containing the trilobites, 

 I have the testimony of Sir W. E. 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 sup- 

 port of the opinion of the most able stratigraphical geologist of 

 the American continent." Paleontology and stratigraphy 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 L^vis 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, including 

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

 crustacean, Conocephalites (^Conocorypht) ininutus, 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 Potsdam sandstone ; 

 while the observations of Shumard in Texas, in 1861, and the latter 

 ones of Hayden 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 Calciferous formations of the New 

 York system. 



As early as 1842, Prof. Hall, in a comparison of the lower 

 paleozoic rocks of New York with those of Great Britain, 

 declared the Potsdam to be lower than the base of the Upper 

 Cambrian or Bala group of Sedgwick. In 1847, as we have seen, 



