408 G. L. COLLIE — ORDOVICIAN SECTION NEAR BELLEFONTE 



Ordovician rocks. The particular section described in this paper extends 

 from the tollgate one mile south of Bellefonte to the entrance of Miles- 

 burg gap, north of the town. The best exposures are at the city laundry, 

 near the Nittany Valley Iron Company's furnace in Bellefonte, and in the 

 northern environs of the town along the Milesburg turnpike. 

 According to Rogers : 



*' The main anticline of Nittany valley is by far the greatest of the Alleghany 

 group. Its length is 130 miles, its width from 15 to 18 miles, and the actual vertical 

 height, if restored, is as much as 20,000 feet." * 



Nittany valley is bounded on the northwest by Bald Eagle ridge, on 

 the southeast b}^ the ridge of Nittan}^ mountain. 



The Ordovician rocks reach a great thickness in the valley. D'Invilliers 

 reports at least 6,000 feet of Ordovician limestones without, however, 

 bringing the bottom beds to the surface.f 



In some portions of Nittany valley, both to the east and to the west 

 of Bellefonte, the axial beds are sandstones which form the so-called 

 " sand barrens." X In the Bellefonte section no sandstone appears, except 

 local lenses at the base of the limestone series. 



The anticline in which the section described is located has gentle 

 southeast dips, while the northwest dips are steep; consequently the 

 anticline is unsymmetrical. Its crest lies close to the northwest border 

 of the valley. 



The Ordovician beds disappear beneath Bald Eagle mountain and do 

 not outcrop again until the Mohawk valley is reached, 100 miles to the 

 north. 



Position and Thickness of the Rocks 



At the crest of the anticline, 1 mile south of Bellefonte, the dips either 

 wa}^ are gentle, not exceeding 8 degrees. On approaching the mountains 

 the dips gradually increase until at the contact of the Trenton limestone 

 and the Utica shale, near Bald Eagle ridge, the dip is 65 degrees. The 

 average direction of dip in the Bellefonte section is north 30 degrees west, 

 although there are numerous local deviations from that direction. The 

 average dip of the Utica shale is 70 degrees north 30 degrees west ; that 

 of the Lorraine shale is between 70 degrees and 90 degrees north 30 de- 

 grees west. The Lorraine shale is frequentl}^ vertical or even overturned, 

 but ordinaril}^ it is less than 90 degrees. The limestones and the Utica 

 shale are situated in the valley ; the Lorraine shale forms the base of 

 the mountains. 



* H. D. Rogers : Geol. Pennsylvania, vol. i, pt. i, p. 467. 

 E. v. d'Invilliers: Pennsj^lvania Second Geol. Snvvej% vol. T. 4, p. .{01. 

 V. u'lnvilliers : Pennsylvania Second Geol. Survey, vol. T. 4, p. M). 



