ROCHESTER AND ONTARIO BEACH QUADRANGLES 17 



with the increasing amount of silt beginning with the deposition 

 of the Rochester shale. The arching of the Rochester shale 

 over some of these masses forms a conspicuous feature of these 

 structures. 



In the Genesee gorge these reefs may be observed at the base 

 of the Rochester shale, not far above the water level, just above 

 the Rome, Watertown & Ogdensburg Railroad bridge. These are 

 the most accessible for examination, though others are found along 

 the gorge and in Palmer's glen. These structures were very favor- 

 able for the existence of other forms of life. Specially is this true 

 of those which in their larval and later form had a fixed mode of 

 life. For such, these reeflike structures offered an excellent place 

 for attachment. 



The number of species already recorded from these reefs is more 

 than 100. Some species occur in large numbers, as for example the 

 brachiopod Whitfieldella nitida and the trilobite Illae- 

 nus ioxus. This trilobite is usually not found complete, but 

 multitudes of cephalic and caudal shields are found closely packed 

 together. Other common forms include Atrypa reticularis 

 Camarotoechia neglecta, Spirifer crisp us, Lep- 

 taena rhomboidalis and C a 1 y m m e n e n i a g a r e n s i s . 

 The affinities of the fauna of the Irondequoit limestone and specially 

 of the lenses, show a close connection with the fauna of the Roches- 

 ter shale. 



Niagara formation. Rochester shale. The term Rochester shale 

 was first used by Hall in 1838. Since that time the term Niagara 

 shale has been frequently applied to this formation, but in the 

 revised nomenclature of the New York rock series by Clarke and 

 Schuchert, the term Rochester shale was revived with its original 

 significance. 



Along the Genesee river this formation forms the top of the gorge, 

 from north of Driving Park bridge, nearly to the upper falls where 

 a few feet of the lower part of the Lockport dolomite are shown. 

 With the exception of these few feet of dolomite at the crest, the 

 whole vertical hight of the falls is made up of Rochester shale. The 

 river bed from below the falls to just below the Vincent street 

 bridge, where the Irondequoit limestone shows, is excavated in this 

 shale. 



