HISTOEICAL GEOLOGY 87 



The New York State Survey, begun in 1836, was con- 

 tinued by James Hall from 1843 to 1898. During this 

 time he was also state geologist of Iowa (1855-1858) and 

 Michigan (1862). Since 1898, John M. Clarke has ably 

 continued the Geological Survey of New York, the state 

 which continues to be, in science and more especially in 

 geology and paleontology, the foremost in America. 



Western Extension of the New York system. Before 

 Hall finished his final report, we find him in 1841 on "a 

 tour of exploration through the states of Ohio, Indiana, 

 Illinois, a part of Michigan, Kentucky, and Missouri, and 

 the territories of Iowa and Wisconsin/' This tour is 

 described in the Journal (42, 51, 1842) under the caption 

 ' ' Notes upon the Geology of the Western States. " His 

 object was to ascertain how far the New York system as 

 the standard of reference "was applicable in the western 

 extension of the series.' 7 In a. general way he was very- 

 successful in extending the system to the Mississippi 

 Eiver, and he clearly saw "a great diminution, first of 

 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, arid 

 Iowa, but unfortunately correlated them with the Niag- 



