204 



Report of the State Geologist. 



Owing to the variable character of the Clinton rocks, the limits of the 

 group are not easily recognized in deep borings, and in most of the well records 

 the strata are partly or wholly included under the term " Niagara " with the 

 next overlying group. 



Niagara group. This group, so named because it is composed of the 

 strata that appear in the face of the precipice at Niagara Falls, overlying the 

 bed of Clinton limestone that comes down to the water level at the foot of 

 the cataract, has two subdivisions, the Rochester shale at the base, here 

 eighty feet thick, and the Lockport limestone eighty-five feet thick, rising 

 above it to the crest of the fall. 



The shale is soft, clayey and slightly calcareous, dark bluish-grey in color, 

 weathering rapidly to a light ashen grey. 



When freshly excavated it has a tough texture with little appearance of 

 a slaty structure, but on exposure it soon separates into small angular frag- 

 ments, and softens into a mass of greyish, marly clay. 



Thin layers of impure limestones occur in the middle and upper parts of 

 the beds, composed largely of corals and other fossils. These fossils are also 

 abundant in the shales. 



The Lockport limestone is best developed in this state in Niagara, Orleans 

 and Monroe counties. At its base there are a few feet of impure limestone, 

 which was formerly burned for water-lime. Above these layers is a bed of 

 light colored crinoidal limestone, succeeded by a darker mass containing 

 geodes, and this again by thin nodular layers of concretionary limestone, sepa- 

 rated by thin partings of carbonaceous shale. 



The limestones are very bituminous and are also magnesian and should 

 be known as dolomites. Geodes are abundant at many localties and contain 

 beautiful crystals of calcite, dolomite, gypsum and celestite. 



The rocks of this formation are exposed on both sides of the chasm 

 between Niagara Falls and Lewiston, and thence eastward in the great lime- 

 stone ridge across the county, where it has been largely opened for quarrying 

 at Lockport and vicinity. 



The chasm at the upper falls of the Genesee river at Rochester has been 

 excavated in this group, and the limestone is extensively quarried in and 

 about the city. The thickness of the Rochester shale is about the same in 

 the gorge of the Genesee river as at Niagara Falls, but the limestone is 

 slightly thinner. Both shale and limestone gradually become thinner toward 

 the east, the belt of which they are the surface rocks becoming narrower as it 

 extends across Monroe, Wayne and Cayuga counties, and the northern towns 



