590 . HENRY SHALER WILLIAMS 



Peculiarities of the formation east of Ithaca. — On passing east 

 of the Ithaca section, into the Dryden and Harford quadrangles, 

 the beginning of the Chemung fauna is found at the same strati- 

 graphic horizon; but the Nunda fauna becomes rare and hmited 

 in range in the Enfield member. The upper limit of the Ithaca 

 fauna proper rises higher in the strata, and a successor of the Ithaca 

 fauna appears in the upper portion of the Enfield, below the Nunda 

 Chemung boundary. In the Chenango valley section there is 

 little, if any, trace of the Nunda fauna above the Sherburne sand- 

 stone, which there represents, as shown by Prosser,' the portion 

 of the Nunda lying below the Ithaca at Ithaca rather than the whole 

 Nunda of the Genesee valley section. In this eastward extension 

 of the portion of the section called "Nunda formation" in the Gene- 

 see valley the species of the Nunda fauna are very rarely discovered, 

 but in place of them an increasing number of species of the Hamilton 

 formation appear, mingled with others of the Ithaca fauna. 



In these strata there are representatives of three faunas, viz., 

 those typically expressed in the Hamilton, the Nunda, and the 

 Chemung formations. In single sections they appear in the order 

 named; but this order of succession can not be interpreted into an 

 assumption that the time range of each is separate. The faunas 

 undoubtedly lap over in time. In stratigraphy this fact is expressed 

 by saying that the stratigraphic horizon at which one fauna is suc- 

 ceeded by the next in a particular section does not represent the 

 same moment of time at which the like succession occurs in some 

 other section. As has been explained elsewhere,^ the principle 

 involved is the geographic shifting of two contemporaneous faunas 

 over the same ground. The fact of this gradual replacement of the 

 Nunda fauna on passing eastward by representatives of the Hamilton 

 fauna is indicated in the Ithaca section by the appearance in the 

 midst of the normal faunas lying above the Hamilton formation of 

 thin beds four times repeated, holding a nearly pure Hamilton 

 fauna. Discussion of this subject will be taken up later. 



1 See Fifteenth Annual Report of the State (New York) Geologist, pp. 112, 113, 

 119, 134, and 221. 



2 Henry S. Williams, "Shifting of Faunas, etc.;" Bulletin of the Geological Society 

 of America, Vol. XIV (1903), pp. 177-90. 



