CANANDAIGUA AND NAPLES QUADRANGLES 17 



careous material increasing toward the top thongh the dark 

 shales pjredominate throughout. The gradual increment of lime 

 content makes the. passage from this bed into that following 

 essentially imperceptible, but there are accompanying notable 

 distinctions in the composition of the fauna. Taking into ac- 

 r-ount a proper allowance for dip it is estimated that the thick- 

 ness of the Cardiff shales is here about 100 feet. 



Skaneateles shale 

 This term was aj^plied by Yanuxem to the beds immediately 

 overlying the upper Marcellus. and exposed on both sides of 

 ^kaneateles lake at the north end. They are evidently con- 

 linuous into the Canandaigua area without essential contrac- 

 tion or change and hence the early term is now employed for 

 them rather than the designation Shaffer shale incidentally 

 used in a recent tabulation of these formations. With the in- 

 crease in calcareous matter the shales become hard, blue black, 

 in places quite black, passing into light and softer beds above 

 with layers of soft impure limestone. For a thickness of 125 

 feet this shale bed keeps its distinctive characters across the Can- 

 andaigua sheet though the distinction is based on comparatively 

 few exposures. These deposits are exposed in the bed of Mud 

 creek south of the highway bridge near the junction of Shaffer 

 creek, J mile north of Wheeler and also along Shaffer creek at 

 J to 5 mile south of Wheeler. A slight exposure of the black 

 shales is also shown in a small drainage section just below the 

 Rolicrtson quarry adjoining the New York Central Railroad on 

 Fort hill in the eastern part of the village of Canandaigua. They 

 are shown in nearly full strength in Miles gully in the town of 

 Hopewell, just east of the east line of the quadrangle. 



Canandaigua shale 



Including the Centerfield limestone at the base 



Two terms which have become ingrained by long usage in the 



nomenclature are the Hamilton group and the LudlowviUe shales. 



The former, introduced by Yanuxem in 1840, was at no time em- 



