wii.uams.] HALL, DE VERNEUIL. 71 



grit, with the Oriskany left out of consideration, and that the line 

 between the Devonian and Carboniferous was not established and 

 should be regarded as a matter for future determination. 1 



Mr. Hall in this review quotes M. de Verneuil's views as to the great 

 importance of the Paleozoic formations of America: 



No series of formations extended in continuous manner over a vaster surface than 

 the Paleozoic strata of North America. * * * 



By one of those happy chances of which the history of science offers us examples, 

 the territory of the State of New York presents us, below the Carboniferous system, 

 the Paleozoic series most complete. Every favorable condition is there also united 

 to facilitate that study, aud to give to superposition, and consequently to paleon- 

 tology, of which it is the foundation, a certainty truly scientific. 3 



Hall as well as de Verneuil objected to the unfortunate grouping into 

 " Champlain, Ontario, etc., divisions " of the rocks of New York. 



The finer subdivisions are, however, of permanent value. As Hall 



wrote : 



In truth, we are satisfied that what has given certainty and security to our labors 

 are the minute subdivisions which have never been attempted elsewhere. 3 



The reason for this is not far to seek. These " minute subdivisions" 

 are the natural stratigraphic units of the rocks and express the his- 

 torical changes of local conditions. They express for each geographic 

 province the epochs of its geologic history and are the units of which 

 the geologic history of the world was built. The fossils they contain 

 are the means by which the history of geographically separate prov- 

 inces may be compared, and, as will be seen by tracing the effect of de 

 Verneuil's work, the coordinating and systematizing of tbe several 

 stages of relative uniformity of condition for each separate province 

 are to be accomplished by a comparative study of the fossil contents. 



The reason for grouping any particular formation with those below 

 rather than with those above is not found in its mineral constitution, 

 nor in its strati graphic condition, but in the character of its fossil con- 

 tents. 



The New York geologists attempted to make groupings of the funda- 

 mental formations based upon their relation to the present geographic 

 features of the surface. This plan failed because there is no natural 

 connection between the two sets of phenomena. 



When de Verneuil discussed the matter with Hall on a basis of the 

 fossil contents of each particular formation for each particular geo- 

 graphic province, a natural classification was reached, which, as far as 

 the state of knowledge permitted, was satisfactory, and which persists 

 because it is based upon facts which have a history, and therefore can 

 be historically classified. 4 



In Tennessee, according to the reports of Troostand Owen, Silurian, 



1 Am. Jour. Sci., 2d ser., vol. 7, p. 231. 



2 Ibid., vol. 5, p. 177. 

 s Ibid., p. 179. 



4 Comparison of the geological features of Tennessee with those of the State of New York, by 

 James Hall ; Proc. Amer. Assoc, 1851, vol. 6, pp. 256-25 9. 



