L26 Ziegler — Siliceous Oolites of Central Pennsylvania. 

 CaCO a + SiO., (solution) 



\ 



+p + t 



SiO s + CaCO, (solution) 



+/», + *, 



CaC0 3 + SiO, (solution) 



The compounds in the black-faced type represent the solid 

 material and the reactions are entirely physical, depending 

 mainly on temperature and pressure. In this connection it 

 may be interesting to note that the CaC0 3 is more soluble in 

 cold than in hot water,* while the reverse is true for Si0 2 . It 

 is, however, more probable that the reaction depends on a 

 change in the character of the solution. Thus if an alkali 

 solution of Si0 2 be acidified by C0 2 in the presence of CaC0 3 

 we get a precipitation of Si0 2 and a solution of CaCO s .f Thus : 



CaC0 8 + alkali solu. SiO, + CO a = SiO, + CaH(CO,), acid sol. 



If the acid solution should again become alkaline the tend- 

 ency would be for the reaction to proceed in the opposite 

 direction. 



There are two theories at present to account for the origin 

 of the bedded oolites. In the first, on the basis of a syngenetic 

 origin they are believed to be the result of deposition by hot 

 springs located on the shore of the Calciferous sea. As especi- 

 ally important in this connection have been considered the large 

 concretionary bowlders of the chert occurring within the area 

 of the oolite. These bowlders, supposed rims of hot springs 

 and geysers, are not found, however, wherever the oolites occur. 

 Thus none of them were observed with the siliceous oolite 

 along Spring Creek nor slightly east of the area of the accom- 

 panying map on Logan Creek. Again in the area of oolite 

 occurrence between Fine Grove and Pine Hall, none occur. 

 Bowlders like those described were found southeast of State 

 College and west of Oak Hall ; but no oolite occurs there. 



The relation of the oolite to the adjacent rocks seems to 

 furnish the best clue as to their origin. Thus we have at least 

 two distinct methods of origin as exemplified in this area. Fig- 

 ure 7 shows the occurrence of fine-grained and pure sandstone 

 layers interbedded in dense, light gray limestone. The sand- 

 stone as a rule is friable and may be crumbled easily by slight 



* Comley, " A. Dictionary of Chemical Solubilities," p. 82. 

 t Reactions observed in the Chemical laboratories of the So. Dak. State 

 School of Mines by Prof. Coolbaugh. 



