HISTORICAL GEOLOGY 89 



aran, while the Middle Devonian about Columbus, Ohio, 

 and Louisville, Kentucky, he referred to the same 

 horizon. The Galena-Niagaran error was corrected in 

 1855, but the Devonian and Mississippian ones remained 

 unadjusted for a long time, and in Iowa until toward the 

 close of the nineteenth century. 



Correlations witli Europe. The first effort toward 

 correlating the New York system with those of Europe 

 was made by Conrad in his Notes on American Geology 

 in 1839 (35, 243). Here he compares it on faunal 

 grounds with the Silurian system. A more sustained 

 effort was that of Hall in 1843 (45, 157), when he said 

 that the Silurian of Murchison was equal to the New 

 York system and embraced the Cambrian, Silurian, and 

 Devonian, which he considered as forming but one sys- 

 tem. Hall in 1844 and Conrad earlier were erroneously 

 regarding the Middle Devonian of New York (Hamilton) 

 as "an equivalent of the Ludlow rocks of Mr. Murchi- 

 son" (47, 118, 1844). 



In 1846 E. P. De Verneuil spent the summer in Amer- 

 ica with a view to correlating the formations of the New 

 York system with those of Europe. At this time he had 

 had a wide field experience in France, Germany, and 

 Eussia, was president of the Geological Society of 

 France, and "virtually the representative of European 

 geology" (2, 153, 1846). Hall says, "No other person 

 could have presented so clear and perfect a coup d'oeil." 

 De Verneuil 's results were translated by Hall and with 

 his own comments were published in the Journal in 1848 

 and 1849 under the title "On the Parallelism of the 

 Paleozoic Deposits of North America with those of 

 Europe." De Verneuil was especially struck with the 

 complete development of American Paleozoic deposits 

 and said it was the best anywhere. On the other hand, 

 he did not agree with the detailed arrangement of the 

 formations in the various divisions of the New York 

 system, and Hall admitted altogether too readily that the 

 terms were proposed "as a matter of concession, and it is 

 to be regretted that such an artificial classification was 

 adopted." De VerneuiPs correlations are as follows: 



The Lower Silurian system begins with the Potsdam, 

 the analogue of the Obolus sandstone of Eussia and 



