Maryland Geological Survey 421 



tinguish the upper conglomerate by the litliological features named. The 

 distinction does not appear to be assured, however, since the lower con- 

 glomerate contains similar flat pebbles, some of which are also jasper. 



Upper Shale and Sandstone Beds. Camarotoechia eximia Zone. — East 

 of the Oakland anticline many of the strata of this division contain much 

 iron hydrate and are discolored by iron stains. Associated with this 

 feature are distinct faunal peculiarities. The fossils are often small and 

 depauperate, while species of restricted range appear. This may be 

 called the Camarota'chia eximia zone from the profuse occurrence of that 

 species in it. 



Eed beds occur in the midst of this division in the region west of 

 Sideling Hill dividing it into three parts as given in the preceding table. 



In the Oakland anticline the conditions seem quite different, little 

 ferruginous material being present in these beds, while they are highly 

 fossiliferous and the species are not depauperate. The stratigraphy of 

 that region has, however, not been worked out in detail because of the 

 imperfect character of the exposures. 



Ckemukg-Parkhead Boundary. — It is very difficult to determine 

 this boundary with precision, owing to the close lithological resemblance 

 of these members. The base of the Chemung is generally marked litho- 

 logically by a distinct increase in the percentage of sandstone, the lower 

 beds of the Chemung usually containing heavy sandstones although this 

 feature is not constant. In some localities red strata appear a little above 

 this horizon. In Washington County the base of the Chemung was drawn, 

 for convenience in mapping, at the top of the upper conglomerate of the 

 Parkhead member. The only assured criterion for the separation of the 

 Chemung and Parkhead is the incoming with the Chemung of the Spiri- 

 fer disjunctus fauna, the most distinctive members of which are Spirifer 

 disjunctus and species of the genera DonviUina and DidmanelJn. 



CatsTcill-Chemung Boundanj. 



Barren red sediments of Catskill type alternate with lighter-colored, 

 fossiliferous sediments of Jennings type in the upper part of the Jennings. 

 Such alternations become quite frequent toward the upper limit of the 



