PENNSYLVANIA SILICEOUS OOLITES 767 



they start from the outer margin of the oolite. The larger interspaces 

 may be filled by irregular granules or fibers not related to the oolites. 



In some instances the nuclei have not been secondarily enlarged, and 

 then the fibrous quartz deposit has started to form at the very beginning 

 of alteration. Apparently the fibrous material and the secondary en- 

 largement have both been formed simultaneously in different grains from 

 the same solution (plate 28, figure 3). These silica solutions seem to 

 have carried iron also, and this has been deposited as the oxide in the 

 fibrous zones together with the silica. In the slides studied by the pres- 

 ent writer this occurred in only minute amounts, but Diller has observed 

 cases in which it formed a thick dense layer around the nucleus. 



The amount of iron present must have been very small, as is indicated 

 by the following analyses, but it must have been deposited simultaneously 

 with the quartz, and this throws an important light on the origin of 

 ferruginous oolites, as will be explained later. 



Analyses of siliceous Oolite from State College, Pennsylvania 



ABC 



SiOa 95.83 98.72 98.26 



Si02 95.83 98.72 98.26 



OaO 1.93 .09 .19 



MgO trace 



KA Na^O .26 .28 



Loss on ignition .34 .54 



100.69 99.95 99.89 



A. Barbour and Torrey : American Journal of Science, III, Volume XL, pages 



246-249. These authors record a trace of MgO in this analysis. It is 

 possible that the minute rhombic crystals in the cloudy zone of second- 

 ary enlargement may be dolomite. 



B. W. Bergt: Gesellschaft Isis in Dresden, Abhandlungen 15, pages 115-124. 



C. Ibid. 



The source of the silica was undoubtedly sponge spicules and diatoms, 

 one or both, or, perhaps, radiolarian skeletons, which were originally 

 either in the same beds as the oolites or in beds adjacent to them. 



The process of siliceous replacement was not a limited phenomenon, 

 as indicated by many of the papers published on this subject, for these 

 siliceous oolites occur not only over many square miles in the vicinity of 

 State College and Bellefonte, but also in the eastern part of the State, in 

 the oolitic beds of the same horizon — as, for example, near Allentown 

 and north of Bethlehem. The chert boulders of the former (State Col- 

 lege) vicinity are not limited in number to a few which might have 



