Report of the State Geologist. 



427 



With the foregoing notes upon the opinions of European palaeonto- 

 logists in reference to the age and equivalence of the Helderberg 

 faunas of New York, we may turn to a brief consideration of their 

 predominating faunal characters. It is necessary to remark, in a pre- 

 liminary way, that the conception generally held by American geolo- 

 gists, of the Lower Helderberg as a Silurian fauna, by implication 

 signifies that it is of i)ost-, or supra-classical-Silurian age, in precisely 

 the sense entertained by Barrande for the Bohemian F, G, H. That 

 the Wenlock and Niagara faunas are essential equivalents will 

 not be seriously questioned. Neither will there be efficient objection 

 to the separation from the typical Lower Helderberg fauna, of what 

 is customarily regarded as its basal member, the Waterlime. The 

 reference of this formation to the Onondaga Salt Group is in accord- 

 ance with the views of Prof. Hall expressed in 1859 * and it has been 

 shown by S. G. Williams f that in the Cayuga Lake section, the Water- 

 lime is complicated lithologically with the upper layers of the Salt 

 Group, and inseparable from them, while an overlying series 

 of impure limestones contains a meager representation of Lower 

 Helderberg species. 



The characteristic fauna of the Waterlime, viz., Merostomatous 

 Crustacea, which nourished under the conditions prevailing during the 

 age of the Salina^ with its land-locked seas and salt-marshes, demon- 

 strates its equivalence with the upper Ludlow and the Tilestones, 

 with which the English Silurian is closed, and we may quote Murchi- 

 son's observation, .to the effect that "wherever these large crustaceans 

 are found, and with them small Lin guise and other fossils, we may be 

 sure that we are at or very near the summit of all rocks to which 

 the term Silurian can be applied, and that the next overlying 

 stratum belongs to the first great era of fishes, the Devonian or Old 

 Ked Sandstone."J. 



For the purposes of the present occasion, the faunas of the Lower 

 Helderberg in their typical development may be considered in their 

 entirety. Indeed, the subdivision of the fauna is essentially a varia- 

 tion in facies accompanying the change in condition and quality of 

 sedimentation. This subdivision either of faunas or strata becomes 

 more obscure the further one departs from the region of typical 

 exposures. 



* Palaeontology of N. Y. vol. 3, p. 387. 



t Sixth Ann. Kept. State Geologist N. Y. p. 10, 1887. 



t Quarterly Journ. Geol. Soc. Yol. xii, p. 24. 



