72 Charles Schuchert — Historical Geology, 1818-1918. 



sandy matter, and next of shale, as we go westward, and 

 in the whole, a great increase of calcareous matter in the 

 same direction." He also clearly noted the warped 

 nature of the strata, the "anticlinal axis," since known 

 as the Cincinnati and Wabash uplifts and the Ozark 

 dome. 



Hall, however, fell into a number of flagrant errors 

 because of a too great reliance on lithologic correlation 

 and supposedly similar sequence. For instance, the 

 Coal Measures of Pennsylvania were said to directly 

 overlap the Chemung group of southern New York, and 

 now he finds the same condition in Ohio, Indiana, and 

 Illinois, failing to see that in most places between the 

 top of the New York system and the Coal Measures lay 

 the extensive Mississippian series, one that he generally 

 confounded with the Chemung, or included in the "Car- 

 boniferous group." He states that the Portage of New 

 York is the same as the Waverly of Ohio, and at Louis- 

 ville the Middle Devonian waterlime is correlated with 

 the similar rock of the New York Silurian. Hall was 

 especially desirous of fixing the horizon of the Middle 

 Ordovician lead-bearing rocks of Illinois, Wisconsin, and 

 Iowa, but unfortunately correlated them with the Niag- 

 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 with 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 



