2 6 M-.W YORK ST A I I. MUSEUM 



These nodules contain fossils with their exterior ornament finely 

 retained, that is, replaced in amorphous silica, while in the dolomite 

 the shell substance has been removed and never replaced. The 

 source of the silica here, as in the like segregations associated 

 with limestone, is probably to be found in the spiculesof spong 



It will thus be seen that with the in. reasing salinity, the Lock- 

 port fauna gave way to the Guelph fauna. At first this condition 

 was only temporary and the Lockport fauna under normal con- 

 ditions once more establishes itself, but is finally displaced by 

 the Guelph fauna which in turn disappears with the formation of the 

 Salina sea. 



The Guelph fauna as a whole presents two distinct types of 

 structure, in that the shells are either large and heavy-shelled or 

 small and thm-shelled. The first of these may be regarded as liv- 

 ing on the exposed edges of the coral reefs and the second in the 

 sheltered places among the coral reefs. It may also he stated that 

 the Lockport and Rochester forms found in the Guelph mostly 

 belong to the smaller type. 



The following is a list of Guelph 1 species which have been found 

 in the vicinity of Rochester. Those marked with an asterisk are" 

 also found lower in the Niagaran of New York. ' 



Corals 

 Zaphrentis cf. racinensis Whitfield *F. gothlandicus Lambe 

 •Enterolasma cf. caliculus Hall F. forbesi Edwards <5r= Haime 



•Diplophyllum caespitosum Hall *Halysites catenularius Unnd 



Heliophyllum sf. * n. agglomeratus Hall 



•Favosites aiagarensis Hall Stromatopora galtensis Dai 



F. hisingeri Edwards <Sr» Haime Clathrodictyum ostiolatum Xicholson 



Brachiopods 

 Crania sf. C ? i„dianensis Hall 



•Dalmanella cf. elegantula Dalman *Spirifer crispus Hisin 



* Rhipidomclla cf. hybrida Sowerby * Whitfieldella nitida Hall 



* Camarotoedlia ? Deglecta /Aril 



Pelecypods 

 Mytilarca eduliformis - & Ruede- Pterinea subplana Hall 



"" locardium sf. 



Gastropods 

 Trematonotus alpheus h Poleumita scaranata Clarke & Ruede- 



Diaphorostoma niagarense // mann 



v v " rl - have . i] • ,i by Clarke 



540 u K ••' Memoir 3 ■■( th State Museum. 



