GUELPH FAUNA IN THE STATE OF NEW YORK II9 



We may compare the conditions of the Guelph sea and the character of 

 its fauna with those of fossil coral reefs which have been clearly recognized 

 in the sediments of other formations. Perhaps the best instances are to be 

 found in the Jurassic reefs of France and the Racine reefs of Wisconsin. 



In France the investigations of Oppel, Niosch, and more specially of 

 the Abbe Bourgeat, 1 whose results are reproduced in condensed form in 

 Felix Bernard's Principles of Paleontology* have shown that reefs were 

 formed at various epochs of the upper Jurassic, and that for every sep- 

 arate coral facies there is always a corresponding muddy or lagoon facies 

 and pelagic facies of the same age, but very different in the character of the 

 fossils. The reef of Valfin is cited in illustration of these conditions. 

 The mass of the reef is described as a limestone of corallic origin ; here 

 and there in the irregular mazes is found the special fauna of the reefs 

 which is here very abundant, and particularly rich in forms showing a thick 

 test " which is in accordance with the fact that, the corals growing in 

 regions beaten by waves, the forms, inhabiting them, must necessarily be 

 provided with a strong power of resistance, while small sized species having 

 a thinner covering are only found in well sheltered places." The fauna is 

 described as follows : " There are of the gastropods numerous Nerineas, 

 Cerithiums, Naticas, Turbos, Pleurotomarias ; of the Acephala, Diceras (13 

 species), Lima, Pecten, Trigonia, Corbis ; regular Echini of the family of 

 Cidaridae." We note that the Pleurotomarias, which appear in the Guelph 

 reef with 14 species, are still prominent upon the Jurassic reefs, the long, 

 turreted, heavy Paleozoic Murchisonias, Loxonemas, Subulites correspond 

 in their habit to the Nerineas and Cerithiums so prominent upon the 

 Jurassic reefs ; and the Poleumitas, so abundant in our Guelph are the 

 Turbos of the later reefs. The Acephala however had not yet attained 

 prominence among the earlier reefs. 



On the east side of the Valfin reefs the coraligenous facies changes, 

 passing by intercalation into marls more and more mixed with clay. This 



T Recherches sur les formations coralligenes du Jura meridional. 1887. 

 2 See translation in N. Y. State Geol. 14th An. Rept. 1895. p. 200. 



