Ill) Zieyler — s'tliami.s Oolites of Central Pennsylvania. 



2. Upper Cambrian Sandstone, 500-600 feet. 



Pure, white sandstone, poorly cemented and friable, rarely 

 quartzitic. Shows distinct, thin, and even bedding. The 

 grains are pure, well-rounded sand. In lower portion, gray, 

 and occasional red to brown, tough quartzite, highly and 

 irregularly cross-bedded. 



1. Upper Cambrian Limestones (base not exposed). 



Oolitic limestones ; dark gray to blue, sandy, and shaly 

 limestones. Bedding planes, distorted, and irregular. Layers 

 of Cryptozoon proliferum abundant, also trilobites and brach- 

 iopods (Dikellocephcdus newtoni and Lingulepis sp. ?). 



The exact number of horizons of siliceous oolite it is difficult 

 to state. In one section of the Beekmantown limestones eleven 

 definite layers were exposed. This section represents only 

 about 139 feet near the top of the formation. Outcrops of the 

 calcareous oolites are not at all rare, but good exposures of the 

 siliceous occur only in a few localities (see fig. 1). As a rule 

 the siliceous oolite occurs in loose fragments in mantle rock, 

 especially in the area indicated, while most of the Beekman- 

 town limestones have been removed by erosion, and only the 

 resistant layers of oolite remain. The sandy area underlain 

 directly by the Upper Cambrian sandstone furnished all the 

 oolite specimens from this locality, which in all cases were 

 fragments of loose bowlders. 



The Structure of the Oolite-bearing Rocks. — As will be evi- 

 dent from the accompanying map, the rocks are folded into an 

 anticline pitch-down toward the northeast. The oldest rocks on 

 the area are hence shown in the extreme northwest corner of 

 the map where Upper Cambrian limestones have been brought 

 up by a thrust fault. From this core northwestward we get the 

 parallel fringes of the younger formations. Nittany Mountain 

 in the southeast corner of the map is the result of a synclinal 

 pitch towards the east. 



Typical Detailed Section of Oolite Rorizon. — The finest 

 section of siliceous oolite occur in the gorge of Spring Creek, 

 four or five miles south of Belle Fonte. The following is a 

 detailed section of the best exposure : 



31. 50 feet. Gray, thin, and irregularly bedded limestone, with 

 edgewise limestone conglomerate, carrying in 

 upper portion Rastrites, near R. barranelL 

 In the basal portion we have a thin layer of sili- 

 ceous oolite, underlain by dense sandy limestone. 

 Dark gray, slightly oolitic limestone. 

 Light gray, very dense limestone. 

 Dense, blue limestone, with conchoidal fracture, 

 carrying black chert concretions. 

 4 feet. Impure, dark gray limestone. 



30. 



2 feet. 



29. 



2 feet. 



28. 



7 feet. 



