114 NEW YORK STATE MUSEUM 



CONDITIONS OF LIFE AND SEDIMENTATION 



DURING THE PREVALENCE OF THE GUELPH FAUNA 

 In surveying the composition of this fauna one is impressed with the 

 fact that irrespective of class divisions, the species on the whole are either 

 large and heavy shelled or diminutive and thin shelled. We may cite in 

 illustration of this the condition among the brachiopods. The Trimerel- 

 lidae including the genera Trimerella, Monomerella and Rhinobolus are 

 notable, not alone for their abundance but as well for their great size 

 and weight. Similarly heavy and abundant in Ontario is Pentamerus 

 occidental! s, but for the rest of the brachiopod species all are not 

 merely small and thin shelled but diminutive, specially those which have 

 been continued forward from earlier existence in the Niagaran fauna. 

 Among the lamellibranchs the Canadian fauna contains, as just noted, 

 the heavy Megalomus in surpassing abundance and another thick shelled 

 species, Goniophora crass a, but the other species in Canada 

 and all in New York are small and insignificant. The gastropods are 

 chiefly long, heavy, turreted shells, but a few are of small size. If a diverse 

 habit of growth is indicated by these differences we find that among the 

 cephalopods more uniform effects are expressed as though uniform condi- 

 tions encompassed and qualified this entire group. The well known habit of 

 life of these creatures would preclude the likelihood of their being subjected 

 to such widely distinct conditions as those which have affected the rest. 

 Of the trilobites all the large species of the Niagaran fauna are absent. 



Professor T. C. Chamberlin, in studying the character of the upper 

 Siluric dolomites of Wisconsin, recognized the fact that the lenticular accu- 

 mulations of the Racine limestone were ancient coral reefs and we shall find 

 on comparison of the phenomena presented by the dolomites in New York 

 with these Racine reefs, with the Jurassic reefs which have been elaborately 

 investigated in France and with conditions of life and sedimentation pre- 

 vailing on existing reefs, conclusive reasons for construing those dolomites 

 as reef formations. 



