50 



Report of the State Geologist. 



In the subsequent New York reports the section at Ithaca has Keen gen- 

 erally referred to as lower Chemung, doubtless in the broader application of 

 the name Chemung as a major term for all the upper Devonian sediments of 

 this meridian. So completely w as the name lost sight of, that in volumes of 

 the Palaeontology of New York, many localities lying w ithin the limits of the 

 Ithaca group, especially as this term w as employed by Vanuxem in the Third 

 Geological District, were cited generally as of the age of the Hamilton shales, 

 though sometimes referred to the Chemung ; and in Dana's " Manual of 

 Geology," 3d edition, 1880, the name Ithaca growp does not appear. 



Up to this date the fauna of this group had received no attention 

 further than that indicated in the foregoing extracts from Professor Hall's 

 reports, and the depiction by Vanuxem of two of its brachiopod species, only 

 one of which is now recognized, Ii&pto&troplvia mucronata. In 1884, Prof. 

 H. S. Williams published an account of the succession of the faunas in the typical 

 section of the Itliaca group ( Bull. No. 3, V . S. Geol. Surv.). This is an important 

 document for the reason, among others, that it clearly shows the presence here 

 in repeated manifestations of two distinct faunas, the one from the west, 

 marked by the presence of goniatites and eardioconchs, and by the absence of 

 brachiopods; the other from the east characterized especially by the prevalence 

 of Hamilton types of brachiopods and lamellibranchs ; the former is the fauna of 

 the typical Portage series of the western sections, the latter is termed by Williams 

 the Itliaca fauna. This is the first precise use of this expression, and it is at 

 once clearly evident that this Itliaca fauna is not the fauna of the Ithaca group, 

 as outlined by Hall, but of only a part of that group. The section studied 

 by Williams shows that here the fundamentally distinct faunas of the east 

 and w est are interleaved and commingled, each encroaching upon the province 

 of the other and, in turn, being invaded by that other, so that in a vertical 

 section the succession presents the aspect of rapid alternations of these faunas. 

 The data given by Williams permit the construction of the accompanying 

 diagram (Figure 5) designed to express the interpenetration of the two faunas 

 along this meridian, it being understood that the interlocking angles are 

 highly exaggerated. The author has distinguished several subdivisions of the 

 eastward fauna but restricts the term " Ithaca fauna" proper, to its uppermost 

 or latest manifestation. The fundamental distinction in the eastern and west- 

 ern faunas is, however, sharply defined from bottom to top, and the eastern 

 fauna, manifesting itself near the base of the series in the Oladoclwnus fauna, 

 ends only w ith t he disappearance of the " Ithaca fauna,' 1 500 or 600 feet below 

 the first appearance of well defined Chemung species. The "recurrent Hamil- 



