Maryland Geological Survey 345 



called the TJnadilla formation,' while farther easfalong the Chenango 

 Valley it is represented by the Sherburne sandstone, Ithaca beds and 

 Oneonta sandstone. When followed eastward, sediments with the litho- 

 logical characters of the Oneonta appear at lower and lower horizons in the 

 Ithaca until the Ithaca fauna disappears. In a similar manner the 

 Chemung fauna above the Oneonta sandstone is driven out until in the 

 Catskill region of southeastern New York the Hamilton formation and 

 fauna are succeeded by the Sherburne sandstone, which is followed by 

 sediments not lithologically different from those of the Oneonta which 

 pass without any break into the similar lithological deposits of the 

 Catskill formation.'' 



Dana in his time division of the Devonian placed the upper or later 

 portion in the Chemung and Catskill periods.^ The Chemung period 

 as defined in his earlier editions of the Manual of Geology was composed 

 of the Portage and Chemung epochs, the TuUy and Genesee being in- 

 cluded in the Hamilton period, and the Catskill period composed of 

 simply the Catskill epoch. In the last edition, however, the Upper 

 Devonian consists simply of the Chemung period at the base of which 

 was the Genesee shale while the conclusion, that the Catskill is a local 

 formation representing a varying thickness of the Upper Devonian, was 

 accepted and so the name disappeared from the elironological list.* 

 Among the names proposed by Mr. Darton for the formations of central 

 Appalachian Virginia and adopted by the United States Geological Sur- 

 vey for the Folios of that region, the Jennings formation, called from 

 Jennings gap and branch in western Augusta County, Virginia, agrees 

 very closely with the Genesee, Portage, and Chemung fonnations of New 

 York. The line of division between the Eomney and Jennings formations 

 was not indicated very distinctly and it was said that they " intergrade 

 through beds of passage." In reference to the correlation of the Jennings 

 foi-mation it was stated that " very few beds are fossiliferous, and they are 



' Amer. Geol., VoL XXXII, 1903, p. 384. 



^For details of this region and the varying lithologic and faunal characters 

 of the formations see Prosser in the 15th An. Rep. State Geol. [N. Y.], 1897 

 [1898], pp. 87-223 and 17th ibid., 1899 [1900], pp. 64-316. 



^Proc. Am. Assoc. Adv. Science, Vol. ix, 1856, p. 14. 



*Man. Geol., 4th ed., 1895, pp. 576, 602. 



