NIAGARA FALLS AND VICINITY 97 



branching seaweed, B y t h o t r e p h i s gracilis, may be found. 

 This occurs also on some of the shaly partings of the limestones. 

 The impressions vary from the slender variety of great delicacy to 

 a coarse one in which th.c frond consists of broad irregular lobes. 



This stratum generally forms a vertical wall with the next over- 

 lying stratum projecting beyond it. 



Clinton upper limestone. In the region of the Genesee river the 

 lower limestone is succeeded by a mass of shale which is generally 

 fossiliferous, and on which lies the upper limestone. In the Niagara 

 region this shale is wholly wanting, the upper limestone resting 

 <iirectly on the lower. The line of separation is however well 

 marked, both by the diverse characters of the tw^o rocks and by 

 the different way in which each resists destruction by atmospheric 

 agencies. The upper stratum is a crystalline and highly fossiliferous 

 limestone, often pinkish in color, though chiefly light gray with 

 yellowish or brownish particles where oxidation has occurred. 

 Portions of the beds consist almost wholly of crinoid stems or 

 joints, which give the rock a coarsely crystalline and sometimes 

 porous aspect. Fossils are abundant in this rock^ though the 

 variety is generally not large. The most common species is a 

 rotund variety of the brachiopod, Atrypa reticularis (fig. 

 112), which is generally very robust and sometimes almost globular 

 in form. Of the other fossils in this rock several Stropheodontas 

 may be mentioned, among them Strop heodonta pro- 

 funda. A number of rhynchonelloid shells occur, readily recog- 

 nized by their pointed beaks and strong plications. Among these 

 are some small specimens of Camarotoechia acinus, a 

 species characteristic of the Niagara beds of the west. It is readily 

 recognized by its smooth umbonal area, and its single plication in 

 the mesial depression or sinus, corresponding to which, on the 

 opposite valve occur two plications. Among the more abundant 

 fossils of this rock are smooth elongate and rather strongly biconvex 

 brachiopods of the genus Whitfieldella. The most common 

 is W. intermedia, but other species occur as well. The thick- 

 ness of this stratum is ii feet. The upper beds of this series con- 

 tain species which on the whole are of a strongly marked Niagaran 



