Ziegler — Siliceous Oolites of Central Pennsylvania. 115 



engaged in field work during the spring and summer of 1911, 

 Mr. Anderson and the author found a number of outcrop- 

 ping beds of siliceous oolite in place. Hence, now for the first 

 time, the exact relation of the siliceous oolite to the rocks of 

 the area can be determined accurately. Similar siliceous oolites 

 occur near Tyrone on the Little Juniata River, and have also 

 been noted by Stosef in the Mercersburg-Chambersburg quad- 

 rangle in the southern part of the state. The geologic con- 

 ditions both at Tyrone and at Chambersburg are essentially the 

 same as in Center County. 



Occurrence and Distribution. — Both calcareous and siliceous 

 oolite occur in Center County. The calcareous oolites, as a rule, 

 are massive oolitic limestones of dark gray to blue color, with 

 small, well-rounded spherules. Occasionally they are also dark 

 gray, slightly crystalline, and have small dark green oolites. 

 The siliceous oolite occurs interbedded in thin irregular layers 

 in the limestone, and also in irregular chert concretions and 

 nodules in some rare limestone layers. As far as observed, the 

 oolite beds are confined to the Ordovician and Cambrian strata, 

 which may be subdivided as follows in Center County : 



1. Utica and Lorraine Shale, 1200 feet. 



Gray, sandy shale, and intercalated, gray, resistant sand- 

 stone layers in upper part. Unfossiliferous. 



Black, fissile, and calcareous shale below, fossiliferous. 

 6. Trenton Limestone, 600 feet. 



Dark black, and blue, blocky limestones with interbedded 

 shale layers and crystalline gray limestones, usually fossil- 

 iferous. 

 5. Black River Limestones, 100 feet. 



Compact, very pure, dove-colored limestone, with few 

 fossils at top, below almost black even-fracturing limestones, 

 fossiliferous. Shaly layers at bottom. 

 4. Chazyan, 2300 feet. 



Compact, dense, light grajr, dolomitic limestone with chert 

 nodules at top, unfossiliferous in part. ] 200 feet shaly lime- 

 stones, interbedded with massive, pure, and crystalline, blue 

 limestones at base. Occasional oolitic limestone beds. Fos- 

 siliferous. 

 3. Seekmantown, 2400 feet. 



Series of highly shaly, laminated limestones, with many 

 shale partings. The limestones, as a rule, are clastic "Edge- 

 wise " and other conglomerates. Shale partings are often 

 ripple-marked and. show suncracks. Fossils rare in upper 

 portion. At base interbedded sandstone lenses. Some 

 oolitic limestone in lower portion, and siliceous oolite layers 

 throughout. ' 



*TJ. S. Geol. Survey, Folio No. 170. 



