414 G. L. COLLIE ORDOVICIAN SECTION NEAR BELLEFONTE 



rocks and those so obscure as to be worthless for purposes of identifica- 

 tion. The first fossiliferous horizon known above the dolomitic lime- 

 stone probably represents the Ridley limestone of the Stones River group, 

 which includes the formations between the Beekmantown and the Black 

 river. The two lower divisions of the Stones river — that is, Murfrees- 

 boro and Pierce limestones — do not seem to be present. The overlying 

 Mohawkian * group includes the Black River and the Trenton forma- 

 tions. 



The thickness of the Stones River and Mohawkian rocks is[949 feet, 

 distributed as follows : Stones River, 253 feet ; Black River, 93 feet, and 

 Trenton, 603 feet. The fossils found in these formations usuall}'" occur 

 in thin zones. They are not distributed generally through the rock, and 

 this is the case especiall}^ in the impure shaly limestones. 



The principal fossils found in horizon A-4 are Bathyurus extans Hall, 

 Leperditia fabulites Conrad, Strophomena filitexia (Hall), and Protorhyncha 

 ridleyana (Safford). 



Horizon A-5 may be regarded as the possible equivalent of the Leba- 

 non limestones as described by Safi'ord. The principal fossils occurring 

 here are Leperditia fabulites and Lophospira milleri (Hall). 



In horizon A-6 the only form found in abundance is Strophomena fiU- 

 texta (Hall). Certain zones are filled with it. It wall be noted that this 

 horizon contains no fossils typical of the Stones River group. It might 

 as well be classed with the Black River formation or be regarded as a 

 transition zone between the Stones River and the Black River. On litho- 

 loical grounds, the author prefers to class it with the Stones River group 

 rather than with the succeeding formation. Horizons A-4 to A-6, in- 

 clusive, are therefore grouped together under the head of Stones River, 

 a group that seems to be in geographical distribution, thickness, and 

 paleontological interest nearl}^ or quite equal to the Trenton limestone 

 itself.t 



In horizon A-7 are found the extensive quarries of the region, which 

 has greatly facilitated the collecting of fossils in spite of the fact that the 

 rocks as a whole are quite unfossiliferous. 



The faunas of this horizon show^ that it belongs to the Black River 

 formation, though in the upper portion basal Trenton forms begin to 

 appear. The principal fossils found are as follows : Trinudeus concen- 

 tricus Eaton, Ceraurus pleurexanthemus Green, Isotelus platycephalus Stokes, 

 Pterygometopus callicephalus (Hall), Ccdyinmene callicephala Green, IlLieniis 

 crassicauda Wahlenberg, Tetranota obsoleta Ulrich, Maclurea bigsbyi Hall, 



*As originally defined by Clarke and Schuchert (Science, vol. 10, pp. 874-878), the Mohawkian 

 includes the Birdseye or Lowville limestone, but Winchell and Ulrich regard the Birdseye as the 

 top member of the Stones River group (Geol. Survey of Minnesota, vol. iii, part ii, p. xc). 



t Winchell and Ulrich : Geol. Survey of Minnesota, vol. iii, part ii, p. xc. 



