Report of the State Geologist. 



435 



In America this group has but a meager representation in the Upper 

 Helderberg (one very rare species), but in the Hamilton it attains great 

 individual abundance. 



Of the Cephalopoda the genera Ascoceras, Lituites, Actinoceras, Ormo- 

 ceras, Streptoceras have no representatives. No form of Gomphoceras 

 is present, either those of Devonian character with simple aperture, or 

 the Silurian forms with the aperture constricted (Pentacoceras, Hexaco- 

 ceras, etc.). Goniatites is absent. This Devonian genus appears first 

 in America, in the Tornoceras Mithrax of the Upper Helderberg. The 

 representation of the genus throughout the American Devonian is 

 extremely meager when compared with its development in the German 

 Devonian, where it ranges through the entire formation with an almost 

 endless series of specific variations. It is, therefore, evident that with 

 the imperfect development of both Goniatites and Gryphceus in our 

 faunas, no such diagnostic value can be assigned them as in faunas 

 where conditions have favored their increase and diversity. 



Among the Lamellibranchs, the genus Ambonychia, Anomalodonta, 

 Tellinomya, Glidophorus and probably Modiolopsis are wanting. 



Of the Brachiopods, the peculiar group of the Trimerellidse became 

 extinct in the Niagara and Guelph fauna, (Trimerella, Monomer ella, 

 Dinobolus, Rhinobolus). No representatives of Eichwaldia, Streptis, 

 Zygospira, Whitfieldia, Rhynchotreta or Platystrophia have been found. 



The foregoing data assuredly indicate a striking development in the 

 typical Lower Helderberg fauna, of organic groups, which in their 

 culmination are characteristic of the Devonian. This consists not 

 merely in the inception here of Devonian types. It is generally true 

 that any fauna embodies various forecasts of those to follow. But in 

 addition we meet here certain climacteric features of critical value, 

 demonstrating equivalence with faunas whose age may be considered 

 now as well established. For example, the development of Dalma- 

 nites (Hausmannia), the Platyceratidse, Phacops of the type of 

 P. fecundus, etc., as in the Hercynian of the Hartz and Erbray. Not- 

 withstanding the absence of the strong Devonian types Gryphceus 

 and Goniatites, these Hercynian characters are endorsed and supple- 

 mented by the inception or broader development of characteristic 

 Devonian groups. 



The Silurian cast of the fauna is, however, still maintained, with 

 fully as much force in negative as in positive characters, and this is 

 certainly in harmony with our expectations in the case of a fauna 

 whioh can not be paralleled with the typical development of those 



