98 NEW YORK STATE MUSEUM 



type, such as Spirifer niagarensis and others. A com- 

 mon brachiopod is S t r o p h o n e 1 1 a patenta, a flat, thin, sub- 

 semicircular shell with a straight hinge line and fine surface 

 striations. 



A characteristic feature of this upper limestone stratum is the 

 strong development of stylolite structures. These stylolites are 

 vertically striated columns, from a fragment of an inch to several 

 inches in length, and ranged on either side of a horizontal suture 

 or fissure plane in the limestone bed. Projecting from both upper 

 and lower beds, they interlock with each other and so produce a 

 strongly marked irregular suture. This structure is characteristic 

 of limestone beds of this type, but its origin is still obscure. 

 Pressure of superincumbent layers of rock seems to have been the 

 chief cause of their production, this pressure acting unequally on the 

 rock mass, from the presence of fossils or from other causes. A 

 characteristic feature is the open suture at the ends of the columns, 

 which gives the layers the aspect of having separated by shrinkage 

 along an irregular plane. The vertical striations indicate motion 

 either upward or downward. 



The Clinton limestones may be seen in both banks of the river 

 where not covered by vegetation, from the mouth of the gorge to 

 within a short distance of the falls, near which they are covered by 

 talus. They always form a cliff in the profile of the gorge, the 6 

 feet of shale below them forming a sloping talus-covered bank, 

 below which there is another cliff formed by the hard upper Medina 

 sandstone, the lower members forming one or more talus-covered 

 slopes down to the quartzose bed of the Medina. This latter is 

 again a cliff-maker, and generally projects from the bank, while the 

 soft red shale below invariably produces a sloping* talus-covered 

 bank. Above the Clinton limestones is another slope and talus 

 formed by the soft Rochester shale, above which a precipitous cliff 

 is formed by the Lockport limestone. 



At the base of the cliffs, fallen rocks of the Clinton limestones are 

 mingled with those from the overlying Lockport limestones, and. 

 care must be exercised in discriminating between these when col- 

 lecting fossils. Halfway between the third and fourth watchman's 



