STRATIGRAPHIC TAXONOMY 653 



at the base — 485 to 570 feet in the former, 530 feet in the latter — is, so 

 far as observed, everywhere relative!}^ non-magnesian. As for the Cana- 

 dian beds above this member, they become even more magnesian in central 

 Pennsylvania. The following generalized review of the Beekmantown in 

 the Chambersburg belt seems desirable here : 



Beginning with the base, which evidently is in unconformable rela- 

 tionship to the underlying Conococheagne formation, there is first the 

 Stonehenge member, consisting of 570 feet of limestone, the lower part of 

 which is massive and dove in color, the middle and most of the upper 

 parts generally of darker color, with contorted argillaceous and siliceous 

 laminations, oolites, and thin bands of intraformational conglomerate. 

 Some large, broadly umbilicated gastropods, allied to Pleurotomaria 

 canadensis Billings, smaller forms of Ophileta, Dalmanella wemplei, and 

 fragments of trilobites, are distributed through the middle and lower 

 parts of the member. 



The next higher division is nearly 800 feet thick. It begins with a 

 60-foot bed of largely oolitic, cherty limestone. This is followed by 300 

 feet of dove, pink, and bluish, fine-grained pure limestone, locally with 

 chert. The division ends with 275 feet of fine-grained, nearly pure 

 limestone, in which are occasional beds of magnesian limestone, and 

 several layers of porous and sometimes drusy chert. Near the middle 

 there is commonly a considerable development of pink, fine-grained 

 marble. Except in thin zones fossils are rare in this division, the more 

 notable forms being Ophileta complanata, Maclurea afpnis, Eccyliom- 

 plialus cf. triangulus, and Bathyurus cf. conicus. Cryptozoon steeli is 

 not uncommon in the lower 100 feet. Compared with the Belief onte 

 section, the Nittany dolomite seems to correspond in a general way with^ 

 this division. 



The third division, 200 to 250 feet thick, consists of blue and dove 

 limestone, cherty in the upper half. At the base a 6-foot blue limestone 

 is filled with rounded quartz grains. Fossils occur rather abundantly 

 and sometimes in good condition. The most characteristic are Dal- 

 manella? cf. electra, large hornlike opercula of the proposed genus 

 Ceratopea (see page 665), Liospira canadensis, Asaplius canal is, Bathy- 

 urus caudatu^, AmpTiion salteri f, and Primitia, gregaria ?. With these 

 occur Maclurea affinis and Eccyliopterns triangulus. Judging from this 

 faunule, this division appears to correspond very nearly with that of 

 ^'Division D" of the Beekmantown in the Champlain Valley. Probably 

 this Pennsylvania occurrence represents an earlier facies of the fauna 

 than the one found at Fort Cassin, Vermont. The Axeman limestone in 



