Summary. 



(1) The fauna of the Ithaca group is a modified Hamilton fauna ; it 

 contains a more abundant representation of unmodified Hamilton species in 

 the meridional section along the Chenango river where the Tully limestone 

 and Genesee slate are absent. The Hamilton features of the fauna are most 

 strongly expressed in the lower part of the group, before the appearance of 

 Spirifer mesastrialis. The fauna of the rock section at Ithaca is not normal 

 and typical but contains an intermingling of Ithaca and typical Portage 

 (Naples) species. The terms Ithaca group and Ithaca fauna are inexact, and 

 their continued employment is at the cost of precision and lucidity. 



(2) The ( )neonta group, comprising sandstones and shales often highly 

 colored with red and green, occupies the upper part of the Portage series as 

 developed along the Chenango valley and eastward. West of this valley these 

 beds rapidly disappear, thinning out and penetrating the upper beds of the 

 Ithaca group and being penetrated by them. Above them lie proemial 

 Chemung faunules. 



(3) AVestward of Cortland county the Ithaca fauna gradually becomes 

 almost totally extinct and is as gradually replaced by the fauna of the typical 

 Portage series (Naples fauna). 



(4) Above the Portage sandstones which cap the typical Portage sec- 

 tions w est of the Naples meridian, are indications of the final appearance of 

 the Naples fauna through a considerable thickness of strata. 



(5) In the Canandaigua lake section the Portage rocks have, probably, 

 not more than one-half the thickness exhibited in the sections through 

 Cortland and Chenango counties. 



(6) The Portage group is a series of arenaceous deposits rej (resenting the 

 geological time which elapsed from the close of the Hamilton period (includ- 

 ing the Tully limestone and a portion of the (fenesee slate, where present) 

 to the opening of the Chemung period. The typical and unmixed fauna of 

 its westerly sections has little organic relation to the proper fauna of the 

 Hamilton shales, the Chemung fauna succeeding, or the Ithaca faunas 

 adjoining on the east. It is an exotic fauna, evidently derived from the 

 west, and making its first appearance in the Genundewah limestone of the 

 Genesee slates. It is the Naples fauna. 



The fauna of the central and east-central sections is an indigenous fauna, 

 and its organic composition stands in the closest relation t<> the fauna of the 



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