GUELPH FAUNA IN THE STATE OF NEW YORK 13 



Shelby faunas, contained in the lower and upper Shelby dolomites. It is 

 furthermore specially noteworthy that of these two manifestations of the 

 fauna, the lower is the purer Guelph, that is, is freer from complications 

 with species occurring in the Lockport dolomites. In the upper bed, how- 

 ever, the presence of such Lockport species is much more pronounced. On 

 the other hand, the intervening Lockport dolomites are wholly free from 

 any evidences of the Guelph species ; though decidedly meager in fossils, 

 yet these are all proper to the horizon in which they occur. Thus the over- 

 lapping faunas are relatively free of complication and intermixture. We 

 note again, as just stated above, that it is not the lower and purer Guelph 

 congeries that appears in the Rochester section ; on the other hand, it is 

 the later association, containing a number of Lockport limestone species, 

 that agrees better in composition with this more eastern development. 



We are thus presented with conclusive evidence of an invasion of the 

 Guelph fauna from the west into western New York, while the Lockport 

 dolomites were being deposited and at about the middle of the period of 

 their formation ; this immigration was of brief duration, failed to acquire a 

 lasting foothold, withdrew without reaching far if at all east of Orleans 

 county ; it thereafter returned with some unimportant modification in com- 

 position, penetrated as far east as Monroe and Wayne counties, while the 

 previous occupant of the field withdrew, not to return. 



At the close of the descriptions of the New York Guelph species we 

 have given tables showing the distribution of the fossils and bringing out 

 the difference in the composition of the early and late appearance of the 

 fauna in the Oak Orchard creek section and the relation of these manifesta- 

 tions to the fauna in Monroe county. For that place we reserve all further 

 discussion of the affinities of the congeries to extralimital expressions of the 



Guelph fauna. 



Niagara county 



The rock exposures at Niagara Falls show 120 feet of limestone and 

 dolomite currently referred to the Niagaran formation. We have been 

 unable to determine the existence of the Guelph fauna in the vertical sec- 



