Il8 NEW YORK STATE MUSEUM 



ably on the former, this unconformity being emphasized by the 

 absence of all Lower Devonic strata in this region, with the excep- 

 tion of thin lenses of sandstone which may be correlated with the 

 Oriskany. The upper surface of the Manlius limestone is knotty 

 and concretionary, producing minor irregularities, but in addition 

 to these there are well marked traces of the erosion of these strata, 

 prior to the deposition of the overlying beds. These traces are of the 

 nature of channels and irregular truncations of the strata, the former 

 in some cases assuming considerable importance. (Fig. 21-23) 



In the east wall of the quarry, 

 not far from the stamp mill, 

 the surface of the Manlius 

 limestone is strongly ex- 



F i g A 21 Unconformable contact between Manlius cava ted, the excavation being 

 and Onondaga limestones, Buffalo cement quarry. > » 



mainly filled by beds of the 

 Onondaga limestone. Be- 

 tween the two limestones oc- 

 curs a mass of shale and 

 conglomerate having a total 

 thickness, in the central por- 

 tion, of something over a foot. The lower 6 or 8 inches are a lime- 

 stone conglomerate, the pebbles of which are fragments of the 

 underlying limestones. These pebbles are flat, but well rounded 

 on the margins, showing evidence of protracted wear. They 

 are firmly embedded in a matrix of indurated quartz sand, 

 which surrounds them and fills in all the interstices. This 

 bed thins out toward the sides of the channel. On the con- 

 glomerate lie about 6 inches of shale and shaly limestone, and 

 these are succeeded by the Onondaga limestone. The width of the 

 channel, which is clearly an erosion channel, is about 18 feet, and 

 its depth is about 3! feet. (Fig. 23) 



From the point where this channel is seen, the contact can be 

 traced continuously for a thousand feet or more eastward, along the 

 quarry wall. It frequently shows a thin shaly bed, often containing 

 quartz grains, lying between the two limestones. 



Not very far from the channel just described, a remarkable "sand- 

 stone dike " penetrates the Siluric limestones of the quarry wall. 



Pig. 22 Erosion of Manlius limestone prior to depos! 

 tion of Onondaga limestone, Buffalo cement quarry. 



