GUELPH FAUNA IN THE STATE OF NEW YORK 7 



" Gault." It is clear from the expressions above quoted that Hall was 

 the first to recognize the faunistic distinction of this association from the 

 Niagaran ; T but the discriminating observations of the Canadian geologists, 

 Logan, Bell and Murray, aided notably in elevating Guelph sedimentation 

 to the dignity of an event separable from the Niagaran. Professor Hall, 

 after extending his studies of the Upper Siluric dolomites over the area of 

 their distribution in Wisconsin, Illinois and Iowa, was inclined, in subse- 

 quent expressions, to caution in respect to the separation of Niagaran and 

 Guelph faunas ; 2 and to these we shall have occasion to refer in bringing 

 the data here presented into harmony with facts previously known. 



The Wayne county, N. Y., locality for " Onondaga Salt group " fossils 

 was long ago lost. Nothing more is known of it than was given by Hall 

 in 1843 ; and no examination of the region in later years has given any 

 clue to exposures of this horizon, but some remarks on the horizon there 

 presented are given in a subsequent paragraph. 



The Lockport or Niagaran dolomite in western New York makes a 

 very clearly defined topographic feature, specially where transected by 

 drainage ways. As is well known it is the rock which is the cap and occa- 

 sion of the falls at Niagara and of the upper falls of the Genesee river at 

 Rochester, and, though modifying the contour between these points, only 

 its lower parts project freely as exposure or lie under slight drift cover. 

 This mass of dolomites, which is not less than ioo feet in thickness 

 between Niagara Falls and Rochester, is at bottom at first comparatively 

 pure and hard, but becomes more and more dolomitic and less resistant 3 

 toward the top. The overlying soft shales, gypsum beds and "platten" 

 limestones of the true Salina have been so worn down by obsequent 

 drainage that south of the Niagara escarpment, which is largely con- 

 stituted of only the lower layers of the Lockport dolomite series, the 



1 See also Pal. N. Y. 1859. 3 : 30. 



• N. Y. State Cab. Nat. Hist. 20th Rep't. 1868. p. 306 (rev. ed. p. 348). 

 3 That is, more yielding to meteoric agency, because the purer the dolomite, in this 

 section, the more completely is it of fragmental origin. 



