DUAL NOMENCLATURE. 153 



On the assumption, which has been the common practice up 

 to the present time, that the divisions of the time-scale and of 

 the list of formations are synonymous', it is reasonable to insist 

 that the Catskill and the Chemung are not correlative terms, and 

 that, in case we apply them as formation names, the one must 

 succeed the other, but I think we all know that this is not the 

 case. We know, that is, that in western New York a continuous 

 section takes us through Hamilton, Portage, Chemung, Con- 

 glomerate and Carboniferous formations ;' that a like section in 

 the meridian of Cayuga Lake takes us through Hamilton, an 

 interval filled with Spirifer levis beds, the Ithaca group and 600 

 feet with Portage fauna, then the Chemung, the Catskill, and 

 finally the Carboniferous. Farther east the interval between the 

 Hamilton and Chemung is filled by rocks with an advanced 

 stage of the Hamilton fauna ; then the Oneonta and next rocks 

 with another stage of the Hamilton fauna, then the Chemung 

 and the Catskill. Still farther east, Chemung drops out from 

 the series ; and if we go on to Maine and Eastern New Bruns- 

 wick, the Hamilton also falls out, and a long series with the 

 latest marine fauna an Eodevonian Oriskany fauna, separated 

 from the Carboniferous deposits by several thousand feet of 

 deposits which, faunally and structurally, may be considered 

 equivalent to the Catskill of New York. It is evident, thus, 

 that at different localities the Catskill formation has a time 

 value in one place equivalent to the closing part of the Chemung 

 formation ; at another place to the whole of the Chemung ; at 

 another to the upper part of the Chemung, and also an earlier 

 stage during the formations of the Ithaca formation ; at another 

 place it represents the whole upper Devonian, and, if we mean to 

 extend the use of the name to Maine, to the whole of the upper, 

 middle, and most of the lower Devonian. 



It is, therefore, clearly inappropriate to use the term Catskill 

 as a name in the time-scale, because it has no common definition 

 in that scale. It is an appropriate local formation name for 

 deposits succeeding Hamilton or Chemung formations in Eastern 



'See the table on p. 155. 



