GUELPH FAUNA IN THE STATE OF NEW YORK 



INTRODUCTION 



TYPICAL GUELPH DOLOMITES OF ONTARIO AND THEIR FAUNA 

 The Guelph formation of Canada has been regarded by geologists as 

 a local stratigraphic development succeeding the Niagara or Lockport 

 limestone and antedating the desiccation of the sea which precipitated the 

 deposits of the Salina stage. The formation in central Ontario, the region 

 of its typical and highest development, has the aspect of a great lentil 

 thinning to the southeast toward the Niagara river and to the northwest 

 at Manitoulin island in Lake Huron, in the interval attaining a thickness 

 of not less than 200 to 300 feet. Whether it is interrupted at this northern 

 point is not determined, but it has recently been shown that certain 

 characteristic fossils of the fauna occur in the territory of Keewatin about 

 James's bay (Equan river) ; Dr Whiteaves has described two species of 

 Trimerella from this region and these seem to indicate the presence of the 

 formation. 1 The actual amount of deposit has however not been accurately 

 measured, and the exposed sections have for the most part proved to be 

 along the quite uniformly northwest strike of the strata. The entire 

 formation is quite completely dolomitized, and this pervading alteration, 

 together with the distinctly fragmental and sandy character of much of 

 the deposit, indicates substantial deviation from the static conditions under 

 which the normal Niagaran fauna was laid down. To the probable origin 

 of these dolomites attention will be directed in a later paragraph. The 

 fauna accompanying this formation has peculiarities of composition which 

 separate it from any earlier manifestation of the Upper Siluric or at least 

 from the Wenlockian fauna of the Niagaran (Rochester) shales and the 

 modified continuation of that fauna into the Lockport limestones of New 

 York. 



It is striking for several of its peculiarities both positive and negative. 

 These may be itemized briefly: (1) The prevalence of holostomatous, 

 probably opercle-bearing gastropods of the genera Coelocaulis, Pycnom- 



1 Ottawa Naturalist [Oct. 1902], p. 139. 



