526 NEW YORK STATE MUSEUM 



sufficient weight. In the study of the vertical distribution of 

 the fauna of this succession, the following points come out with 

 clearness. 



Of these 13 columns no. 8 represents the Wolf creek conglom- 

 erate and no. 6 the Mount Hermon conglomerate. It is the 

 former which proves to be the important line of change in the 

 succession of the faunas. It is to be understood that there is no 

 evidence in this undisturbed and unfolded region of any abrupt 

 change by sudden extinction of species or by unexpected invasion 

 from east or west, but the succession has gone on without inter- 

 ruption and it is only at that horizon where a decided change 

 becomes noticeable without the extinction of all preexisting 

 forms. 



1 Up to' the Wolf creek conglomerate the common Chemung 

 species seem to prevail. For example, Spirifer disjunc- 

 tus, Athyris angelica, A. cora, Chonetes 

 scitula, Orthis tioga, Orthothetes chemung- 

 e n s i s , Productellas of various species, Mytilarca, Nucula 

 bellistriatra, Aviculopectens, Crenipectens, Edmondia, 

 some of the Leptodesmas such as L. p o t e n s and var. 

 juvenis, L. mortoni, L. sociale, Pterinopecten, 

 some of the gastropods like Bellerophon maera, 

 Euomphalus hecale, Macrochilina and the Dictyo- 

 sponges. 



2 Some characteristic Chemung species pass this limit. Thus, 

 for example, Spirifer disjunctus, which is usually re- 

 garded as an index fossil of upper Devonic time, extends beyond 

 the Wolf creek conglomerate up to and within the shales 

 beneath the Olean conglomerate, becoming however of very rare 

 occurrence in horizons above no. 8. Camarotoechia 

 contracta is recorded from all horizons from the base up 

 to and into the Mount Hermon or Salamanca conglomerate. 

 Such species as these however, of which we have cited the most 

 striking instances, must be looked on in the face of the rest 

 of the evidence as having their value as diagnostic of Devonic 

 time modified bv the introduction before their extinction of a 



