PENNSYLVANIA SILICEOUS OOLITES 761 



that by Hovey.^* He evidently had only a few hand specimens of , the 

 material to work with and they were siliceous throughout. His conclu- 

 sion in regard to the origin is stated thus : 



"The rock was evidently made from clear quartz sand by the action of alka- 

 line waters depositing silica in the form of chalcedony around the fragments 

 or aggregates of fragments of quartz and making the cement between the 

 spherules of the same substance, while some of the quartz grains were caught 

 in the chalcedony without being made the nuclei of spherules" (loc. cit.). 



In 1897 Wieland assigned the origin of these oolites to hot springs. 

 He found associated with them peculiar chert boulders, which he consid- 

 ered to be the actual rims of hot springs and geysers on the shore of the 

 sea where these accumulated. He thought that the silica first deposited 

 would form rings, but that deposited while in more rapid motion would 

 form the spherical oolites. 



The following year a very good description, with illustrations, was pre- 

 pared by J. S. Diller and published in Bulletin 150 of the United States 

 Geological Survey. Diller called attention to the work of previous 

 writers, but did not add anything new in the way of explaining the origin 

 of these oolites. 



This subject seems to have attracted no further attention until it was 

 again brought before the geologists of this country in a paper by Moore, 

 originally read before the British Association in 1911, and later pub- 

 lished in the Journal of Geology.^^ In this he clearly demonstrated that 

 when found in place these siliceous oolites were derived from original 

 calcareous oolites. He described and figured microsections which showed 

 various stages of gradation from complete calcareous oolites to wholly 

 silicified grains. He thus substantiated the original explanation of Bar- 

 bour and Torrey, that these were altered calcareous oolites. 



A few months later another paper appeared by Ziegler, in which he de- 

 scribes what he calls several distinct types of siliceous oolites, and while 

 he accepts Moore's explanation of the origin of one of the types (and 

 this was the type investigated by all of the previous writers), he offers 

 another explanation for the other types. He believes that many of these 

 siliceous oolites were formed from pure quartz sands cemented and 

 changed to siliceous oolite by silica-laden solutions subsequent to their 

 deposition and after they were covered with limestones. But in order to 

 account for the perfect concentric oolites he assumes that some of the 

 sandstones already consisted of sand grains concentrically enlarged by 



8* E. O. Hovey : Bull. Geol. Soc. Am., vol. 5, 1894, pp. 627-629. 

 86 E. S. Moore: Jour. Geol., vol. xx, 1912, pp. 259-269. 



LV — Bull. Gbol. Soc. Am., Vol. 25, 1913 



