308 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



mentation of this cycle, was termed the "Portage or Upper Fucoidal group/' many of the layers 

 containing vertical annelid an borings filled with mud, which Iiave commonly passed under the 

 name of Fucoides verticalis. 



In recognition of the fact that the distinction thus instituted in parts of this series would 

 be difficult of application in actual practice, the same author, in 1843, applied the term "Portage 

 or Nunda group" to the entire series lying between the uppermost beds of the Genesee slate 

 and the upper limit of the heavy beds of Portage sandstones. Since that date not only have 

 the rock strata thus delimited in these western sections of New York been known in geologic 

 literature as the "Portage group," but this term has been also, and properly, applied to all 

 formations in whatever sections of this State and bearing whatever faunas, between the horizon 

 of the Genesee slate beneath and the earliest strata characterized by the incoming Chemung 

 fauna above. 



Recent investigations indicate that the historical delimitation of the Portage group in the 

 typical Genesee section does not express the complete upward range of the fauna of this group. 

 In the Genesee Valley the Portage sandstones are overlain by sandy shales and thin sandstones 

 from 100 to 200 feet in thickness and in lithologic character, not unlike the Gardeau layers 

 beneath; and through these beds the Naples or Intumescens fauna ranges, with slight accre- 

 tions. Strictly speaking, this fauna is mainly confined to the more argillaceous layers, while 

 toward the top a Chemimg fauna appears in the more arenaceous strata. But this alternation 

 concerns only the upper portion of these beds. To this series of strata representing the pro- 

 longed existence of the Naples fauna the term Wiscoy shales and sands has been applied. In 

 protracting, upon the evidence of the contained fossils, the scope of the Portage group to include 

 these beds, we shall not appear to violate propriety, for they did not escape the observation of 

 Prof. Hall, who at the close of his description of the Portage group says (1843, p. 248): "The 

 Portage sandstone is succeeded by olive shaly sandstone and shale and this by black micaceous 

 slaty shale with septaria; to this follow shales and coarse sandstones with fossils of the Chemung 

 group." 



In the pages succeeding this quotation and in the second part of his contribution 

 on the Naples fauna ^^ Clarke describes and illustrates with maps the stratigraphy, 

 paleontology, and geography of the later Devonian of New York. 



The "Ithaca group" was early distinguished by Hall, but later ^^'^^ included by 

 him in the Chemung in the following terms : 



In the annual reports this name was adopted for designating the highly fossilif erous shales 

 and shaly sandstones, so well developed at the inclined plane of the railroad and on the Cas- 

 cadilla and Fall Creeks, near Ithaca. Subsequently an examination of the highly fossiliferous 

 strata along the Chemung River, and particularly in Chemung County, resulted in the adoption 

 of that name as designating this portion of the system. 



Succeeding examinations satisfied me of the identity of the formations at Ithaca with 

 those of Chemung, and this opinion was advanced in the annual report of 1841. 



The reasons for merging the two in one were stated to be the impossibility of identifying 

 them as distinct by any characteristic fossils. The same opinion is still entertained, after a 

 full examination of the strata and a comparison of the fossils collected here and elsewhere in 

 well-authenticated localities of the Chemung. There is scarcely a fossil known at Ithaca which 

 is not foimd at numerous othpr localities ; though it is true, not only of Ithaca but of many other 

 places, that some of the fossils are confined to the single locality in which they occur. 



By careful and extended examination the Chemung group may be subdivided locally 

 where it is most perfectly developed, but these divisions will hold good only over small dis- 

 tricts of country, position and lithological character having had much effect in producing these 

 distinctions dependent on fossils. 



