MARYLAND GEOLOGICAL SURVEY 101 



In Maryland and southern Pennsylvania, the Beekmantown strata fol- 

 lowing the Stonehenge member are so uniform in lithologic character 

 that their separation into distinct formations is impracticable. In the 

 Nittanny and other valleys in central Pennsylvania the corresponding 

 strata not only attain a much greater thickness, but also are so developed 

 that four formations are readily distinguishable. These are, in ascending 

 order, (1) the Stonehenge limestone at the base with a thickness of 

 662 feet; (2) the Nittanny dolomite, 1267 feet thick, cherty and holding 

 the Cryptozoon steeli fauna in its lower part; (3) the Axeman limestone 

 158 feet, and (4) the Bellefonte dolomite 2145 feet thick. The entire 

 series, with both overlying and underlying formations, is to be seen in 

 excellent and practically continuous exposures at Bellefonte, Pennsyl- 

 vania. As this section gives the maximum known development of the 

 Canadian system in the Appalachians, the four formations into which it 

 has been divided as above by Ulrich have been adopted in the general 

 time scale. 



Cryptozoon steeli Zone. Following the Stonehenge member, which has 

 just been described, are 600 or more feet of cherty oolitic limestones, dove- 

 colored, fine-grained pure limestone and usually dense textured pink 

 marble. The basal 60 feet consisting mainly of oolitic cherty limestone 

 contains the characteristic fossil of this division a globular mass, com- 

 monly four to eight inches in diameter composed of concentric layers 

 and supposed to represent the secretion of calcareous algae to which the 

 name Cryptozoon steeli has been applied. Though doubtless calcareous 

 originally, these rounded masses are now almost without exception more 

 or less completely replaced by silica in the' form of chert. This fossil 

 occupies a similar position in the Beekmantown throughout the Appa- 

 lachian Valley and it is so abundant and characteristic that this division 

 is termed the Cryptozoon steeli zone. Subaerial decomposition of these 

 particular strata leaves a light reddish residual clay and soil containing 

 an abundance of ordinary yellow "platy chert besides the numerous rounded 

 silicified masses of Cryptozoon. These cherty residual masses unfailingly 

 identify the outcrop of this zone. It is particularly well exposed in the 



