THE DEVONIAN SECTION OF ITHACA, N. Y. 591 



The members 0} the Nunda formation at Ithaca. — From these 

 facts the conclusion is drawn that the stratigraphic equivalent of 

 the Nunda formation of the Genesee valley is represented in the 

 Ithaca section by three subdivisions or members, viz., Sherburne 

 flagstone member, which is the westward extension of Vanuxem's 

 Sherburne flagstones of the Chenango Valley; Ithaca shale member, 

 the equivalent of Vanuxem's Ithaca group; and Enfield shale mem- 

 ber, a member not recognized by Vanuxem or Hall, but first reported 

 by Williams in Bulletin No. j of the United States Geological Sur- 

 vey (p, 30) in 1884 as "Upper Portage." The name "Enfield" 

 is proposed for its outcrop in the town of Enfield, west of Ithaca, 

 The rocks of the Enfield are shales, flags, and thin sandstones as 

 in the Sherburne; the fauna is similar to that of the Sherburne 

 flags below; and the thickness in the Ithaca section is from 600 to 

 800 feet. 



Two reasons may be given for not recognizing the original sub- 

 divisions of the Nunda in the Ithaca section, (i) Though the 

 lithologic characters upon which these three members (i. e., 

 Cashaqua, Gardeau, and Portage) were founded become more 

 pronounced going westward, on passing eastward before reaching 

 Ithaca they fail to be distinctive of the lower, middle, and upper 

 portions of the formation. (2) The fauna which was recognized 

 by Hall in 1843 ^^ characteristic of the Cashaqua member prevails 

 throughout the Nunda formation of the Ithaca section. Hence 

 the subdivisions of Hall's original Portage or Nunda group are 

 ■discarded in the definition of the Ithaca section. 



Discrimination of the members. — The Ithaca member is recog- 

 nized on the basis of its fauna; the portion of the Nunda lying below 

 the Ithaca member is correlated lithologically and stratigraphically 

 with the Sherburne flagstone member of Vanuxem, and the upper 

 portion, lying between the Ithaca member and the base of the Che- 

 mung formation, is for the first time given a distinctive name, i. e., 

 the Enfield member. Lithologically and paleontologically the 

 Sherburne flagstone and the Enfield shale or flagstone are very 

 similar; stratigraphically they are separated by the shaly member 

 bearing the characteristic Ithaca fauna. The range of this Ithaca 

 ^auna is restricted to a zone of about 80 feet in the Watkins expo- 



