Maryland Geological Survey 429 



while many brachiopods appear both within and below them. Vanuxein ^ 

 drew the base of the Chemung at the base of the more arenaceous sedi- 

 ments and called the braehiopod-rich horizon below the Chemung the 

 Ithaca, while the brachiopod-poor shale beneath the Ithaca was named 

 the Portage or Xunda. Hall ' drew the base of the Chemung of central 

 New York at the base of the brachiopod-rich fauna including Vanuxem's 

 Ithaca and Chemung in his Chemung, as shown by his use of that term in 

 the systematic volumes of the Paleontology of New York. 



It was later shown by Williams" that the Naples fauna recurs above 

 the Ithaca, a result which led to the separation of the Ithaca from the 

 Chemung and its inclusion in the Portage group. Williams later * 

 defined the Chemung formation as the strata through which the Spirifer 

 disjunctus fauna prevails. 



In 1897 Clarke ' showed that the Chemung fauna makes its first ap- 

 pearance in the Genesee River section, above the Wiscoy shale Avhich 

 overlies the Portage (Nunda) sandstone, while in the Naples section, 

 further east, it appears at a lower horizon, being found in the Portage 

 sandstone. In 1905 ° Clarke accordingly proposed to restrict the term 

 Chemung to strata of the age of those bearing the Chemung fauna at 

 the type locality and which lie above the horizon of the Wiscoy (Pratts- 

 burg) shale, excluding the latter from the Chemung. 



Williams' has since proposed to employ the term Chemung in a dual 

 sense, calling the sediments containing the Spirifer disjunctus fauna, 

 " the faunal Chemung " and the arenaceous sediments of which it is a 

 part, " the lithological Chemung." 



The usage of the various aiithors, as applied to these sediments in cen- 

 tral New York, except that of Clarke, is shown approximately in the fol- 



' Geology Third District, Geology of New York, p. 179, 1842. 

 ' PalfEontology of New York, vols, iv, v, vli. Refers Ithaca fossils to Che- 

 mung. 



^ Bull. U. S. Geol. Survey, No. 3, 1884, p. 20, also Bull. No. 41, 1887, pp. 81-82. 

 *Bull. U. S. Geol. Survey, No. 210, 190.3, p. 82. 

 'Rep. N. Y. State Geologist for 189(3, p. 33, 1899. 

 " Bull. N. Y. State Museum, No. 81, 1905, p. 20. 

 • Folio U. S. Geol. Survey, No. 1G9, 1909, p. 12. 



