582 HENRY SHALER WILLIAMS 



Hamilton -group; and the upper portion contains the different sandstones 8.nd 

 shales below the rocks at Ithaca, subsequently to be mentioned, and the Ithaca 

 and Chemung groups. The distribution of the rocks of the upper part of the 

 Erie division, under the heads of Sherburne flags, Ithaca group, and Chemung 

 group, was founded upon observations made with Mr. Hall, commencing along 

 Cayuga Lake, going south from Ludlowville by Ithaca, and from thence to the 

 Pennsylvania line. The rocks, therefore, along that section, especially the 

 upper ones, are the standard of reference, or types of those of their name. 

 (P. 170.) 



From this quotation it is evident that this section was adopted 

 by Vanuxem and Hall as the standard section, and its subdivisions 

 as the standard subdivisions, of that portion of the geological column 

 which was then called the Erie division of the New York system. 

 The nomenclature applied by Vanuxem to this standard section, 

 expressed in tabular form and in natural order of sequence, is as 

 follows : 



Catskill division 28 Catskill group 



27 Chemung group 



26 Ithaca group 



25 Portage or Nunda group 



Erie division (24 Genesee slate 



23 Tully limestone 

 22 Hamilton group 

 21 Marcellus shales 



Helderberg division .... 20 Corniferous limestone, etc. 



The rocks considered in the present paper are the upper four 

 subdivisions of the Erie division of the New York system. 



Original application of the term "member.''^ — The terhi "member" 

 was used in the text, both by Vanuxem and Hall, to designate a 

 subdivision of a group which offered some local distinguishable 

 characters, but was not regarded as of sufficient importance to incor- 

 porate in the nomenclature of the general classification proposed. 

 Thus, in describing the Hamilton group, Vanuxem says: "This 

 group takes its name from the town of Hamilton, in Madison County, 

 which contains no other rocks, and where the best opportunity 

 exists for examining some of the important members of w^hich it 

 is composed;"' and Hall, in describing the fossils of the Cashaqua 

 shale, says: "In the Cashaqua shale, or lower member of this group, 

 there are several species of shells which have not been seen in any 



I Geology oj the Third District, p. 150. 



