and South Central Pennsylvania. 415 



present but they are exceedingly rare and their worn 

 and comminuted appearance suggests that they have 

 been carried some distance. In the finer portions of the 

 ground-mass the grains of calcium carbonate are some- 

 what obscured by a thin brown film which has the ap- 

 pearance of being either iron-oxide or carbonaceous 

 material. It is interesting to note that, aside from spec- 

 ulations upon this " brown film," there is no evidence 

 which would lead one to suppose that the pure limestone 

 of the quarry beds had been formed by organic agencies. 

 The following analysis of the quarry-rock shows the 

 total amount of variation which has been encountered in 

 several hundred samples taken during the quarry opera- 

 tions of the last few years and collected along the quarry 

 line from Belief onte to Tyrone : 



Si0 2 0-62% 0-94% 



(Al, Fe) 2 3 0-32 0-40 



CaC0 3 97-81 97-60 



MgCOg 1-27 1-06 



The Valentine limestone is so low in silica that it can- 

 not be used for cement. Its purity makes it extremely 

 valuable for chemical purposes, little or none of it being 

 used for flux or the manufacturing of structural mate- 

 rials. It is interesting to consider the analysis given by 

 Vauglian (12) for the finely divided calcareous muds 

 occurring in the Marquesas and Bahamas lagoons : 



Bottom sample 

 one mile west of 

 Bottom sample, west end of 



east side Marquesas South Bight, 



lagoon, Florida Bahamas 



Si0 2 1-18% :.. 0-29% 



(Al, Fe) 9 3 0-37 0-15 



MgC0 8 2-88 2-72 



CaC0 3 95-57 96-84 



Vaughan's description of the finely divided muds from 

 the stagnant area of the South Bight and also from the 

 flats one mile to the west of the west end of the South 

 Bight is particularly significant. He mentions Drew's 

 researches, in which the latter found that the mud off 

 Andros Island contained 160,000,000 bacteria (Pseudo- 

 monas calcis) per cu. cm. but was characterized by al- 

 most complete absence of other organisms. Drew states 



