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NEW YORK STATE MUSEUM 



of the species found by them at the various horizons in the rocks 

 throughout the regions mentioned, which virtually cover the extent 

 of the formation. 



The material on which the identifications here following are based 

 does not include or have reference to that collected either by Pro- 

 fessor Prosser or the writer. Some uncertainties having arisen as to 

 the exactitude of identifications and comparisons and also with ref- 

 erence to the precise horizon of some species, collecting operations 

 were begun dc novo in 1900 in this territory by Mr Luther and the 

 following localities are those from which material was then acquired. 

 The suite of fossils obtained was very extensive and much of it the 

 best in quality that the rocks have afforded. 



It has been well recognized and often referred to in the pub- 

 lished papers of Professor Prosser and the writer that this fauna 

 is at first a repetitive occurrence of the Hamilton fauna beneath, 

 shades of difference in the species above and below the horizon 

 of the Tully limestone and Genesee shale and Sherburne sand- 

 stone being at first absent or obscure, but becoming more pronounced 

 upward in the series and accompanied by the introduction of species 

 alien to the fauna below. Broadly it may be said that the fauna 

 starting at the base of the Ithaca sedimentation is essentially Ham- 

 ilton but by degrees, by the addition of species and through muta- 

 tional and profounder variation from the ancestral species, puts on a 

 different aspect and gradually assumes that of the higher or Che- 

 mung fauna. The constituents of the fauna as here tabulated have 

 been made up with the greatest care and extraordinary precaution 

 with an eye keen to the detection of departures from the specific 

 types. 



We have found thus far no good basis for a division of these sedi- 

 ments either on lithologic or faunal characters, hence, for conveni- 

 ence in indicating the relative position of the species, have indicated 

 an upper and lower division quite perfunctorily, taking as a dividing 

 line the middle of the section in the different meridians. The dis- 

 tinction in elevation is noted in the locality numbers following the 

 species names, the higher horizons being printed in heavier figures. 

 The fauna in point of number is prevailingly affiliated to that of the 



