and South Central Pennsylvania. 417 



Pseudomonas colds. The validity of Vaughan's specu- 

 lations regarding the precipitation of calcium carbonate 

 by inorganic agencies is not yet fully established, and 

 these agencies may also ultimately prove to be important 

 factors in the formation of both calcium and magnesium 

 carbonates. 



Center Hall Formation. — In order to procure fresh 

 quarry-rock uncontaminated by the talus which accumu- 

 lates from the argillaceous limestones of the hanging- 

 wall, the American Lime and Cement Co. has sunk a 

 shaft in the purest, upper beds of the Valentine, and is 

 now removing considerable rock by the stoping method. 

 The width of the stope is at present limited by the shaft 

 in the basal beds and by a much less pure zone which it 

 does not pay to quarry. The line of contact between the 

 pure and impure zones above is shown to be gradational, 

 and the upper beds are fairly fossiliferous, the most 

 important fossils being Columnaria no v. sp., Maclurites 

 logani, and one or two species of simple corals. Colum- 

 naria has been observed on the hanging-wall of the 

 northernmost quarry at Belief onte but it does not appear 

 to be as abundant at this horizon. To this narrow zone, 

 which occurs above the Valentine and below the highly 

 fossiliferous and lithologically dissimilar Rodman, I have 

 given the name Center Hall, after the village of that 

 name in Penns Valley. The Center Hall formation is 

 only a few feet thick along the Tyrone-Salona line, but 

 it appears to thicken eastward, possibly replacing the 

 upper beds of the Valentine. It is impossible to state 

 definitely at the present time whether or not the Center 

 Hall can be distinguished from the upper Carlim in the 

 eastern sections. There is good evidence, however, that 

 it can not be distinguished at Thorpe's Quarry. 



The taxonomic problem of the Stones River forma- 

 tions is a serious one, which will have to be solved, not 

 only for this area, but for numerous sections throughout 

 the Appalachian geosyncline. If one were describing a 

 single section along the Tyrone-Salona line he would be 

 correct in giving f ormational names to the pure ' ' quarry- 

 rock'' and the thin but exceedingly distinctive zone 

 directly underlying the Salona (basal Trenton). Neither 

 of these formations, it is true, is of mapable thickness, 

 but the Valentine is of great commercial importance and 

 therefore should be shown at least on the economic sheet 

 of a geologic folio. The term Rodman has already been 



