428 Williams — Fossil Faunas and their use in 



the Tropidoleptus fauna although there are a considerable 

 number of so-called Hamilton species in the Ithaca formation. 

 As this latter formation is traced eastward, however, the 

 species of the Tropidoleptus fauna increase in it, and the 

 dominant Tropidoleptus species take higher bionic rank ; so 

 that the fauna of the Ithaca formation, in its eastern extension, 

 contains two of the standard dominant species of the Hamilton 

 formation among its twelve dominant species as evidenced by 

 67 faunules. 



That this Productella fauna is actually distinct and younger 

 than the Tropidoleptus fauna is shown by the fact that there 

 are 21 species in it which are characteristic of the Ithaca 

 formation at Ithaca which is known to be above (by several 

 hundred feet) the top of the Hamilton formation and Genesee 

 shale. These 21 species are not known to occur in the 

 Hamilton formation in any of its exposures ; and among them 

 are seven of the ten most dominant species of the Ithaca 

 formation. 



If a step be taken further westward, it is known that the 

 total sediments (of some 1000 feet thickness) from the top of 

 the Genesee to the true Chemung, with its Spirifer disjunctus 

 fauna, in the Genesee valley, contain none of the dominant 

 species of either the Hamilton or Ithaca formations ; I refer 

 to the typical Portage formation. 



Again, we have positive evidence of a colony of the 

 Tropidoleptus fauna within at least fifty feet of the typical 

 horizon of the Chemung formation in Chemung County ; and 

 also in the midst of the Chemung or Spirifer disjunctus fauna 

 at Owego, as I announced in 1884.* 



These evidences of the Tropidoleptus fauna are so clear that 

 if we were to find them in an isolated region, no hesitation 

 would be taken to calling the formation holding them 

 Hamilton, except that a few species of much later age are 

 associated with them. 



The typical species of the Tropidoleptus fauna are such as 

 Tropidoleptus carinatns abundant, 

 Amboeoelia umbonata " 



Phacops rana rare but with several specimens. 



It also contains such characteristic species as 



Spirifer marcyi, and probably S. granulosus, 



Cypricardella bellistriata, 



Goniophora hamiltonensis, 



Macrodon hamiltonice, 



Loxonema delphicola, and 



Modiomorpha mytiloides. 



*Bull. 3, U. S. Geol. Survey, p. 24, 1884; also Proc. A. A. A. S., xxxiv, 

 p. 226, 1886, — this is the stage A 6 + of the Tropidoleptus fauna, called in that 

 paper Middle Devonian fauna A ; also p. 230. 



