Ziegler — Siliceous Oolites of Central Pennsylvania. 113 



Art. XI. — The Siliceous Oolites of Central Pennsylvania ;' x " 

 by Victor Ziegler. 



Contents. 



Summary of Previous Work 113 



Occurrence and Distribution 115 



Structure of the Eocks 116 



Typical Detailed Section of Oolite Horizons .. 116 



Petrographi e Description 118 



Origin of the Oolite 124 



Summary 127 



Summary of Literature. — The occurrence of siliceous 

 oolite in Center County, Pennsylvania, was first noted by 

 Rogers in the report of the First Geological Survey of Penn- 

 sylvania. In a brief statement. Rogers calls attention to 

 the extreme scarcity of oolitic chert and its occurrence here. 

 D'Invilliers in the report on Center County, of the Second 

 Geological Survey of Pennsylvania, also merely calls attention 

 to this occurrence, and notes the presence of oolitic limestone 

 in this region. Barbour and Torrey, in 1890, f first gave a 

 description of the structure of the siliceous oolite as revealed 

 by the microscope, and analyses of the same. To E. 0. Hovey, 

 however, belongs the credit of making the first thorough study 

 of these rocks and of first applying the petrographic micro- 

 scope to their interpretation. Hovey:]: arrives at the conclu- 

 sion that the oolites are the result of deposition from the silica- 

 laden waters of hot springs about a nucleus of sand. Wieland,^ 

 in 1907, discussed briefly this and related oolitic rocks and 

 arrived at the same conclusion as Hovey in regard to their 

 origin. As especially important he regards the occurrence of 

 chert bowlders of peculiar concentric structure in the area of 

 less than one square mile within which the oolites are found, 

 These he considers "the rims of hot springs and geysers on the 

 low-lying shore of the Calciferous." Wieland states that " the 

 dissolved silica first deposited would have formed rings ; that 

 deposited while in more rapid motion the small spheruled 

 oolite, which is most plentiful near the best marked of the rim 

 bowlders. Lastly would be formed large-grained oolite, the 

 compact and pure quartzite, which is the handsomest oolite 

 known." E. S. Moore, in a paper read before the British Asso- 

 ciation for the Advancement of Science in 1911, regards the 



* The thanks of the author are due to Professors James F. Kemp and C. P. 

 Berkey for kind and valuable suggestions, 

 t This Journal (3), vol. xl, p. 246. 



% Bulletin of the Geological Society of America, vol. v, p. 627. 

 § This Journal (4), vol. iv, p. 262. 



