Brown — Silurian Limestone of Milesburg Gap. 83 



Art. IX. — Notes on the Silurian Limestone of Milesburg 

 Gap, near Belief onte, Pennsylvania • by Thomas C. 

 Brown. 



In the central part of Center county from Bellefonte north- 

 west through Milesburg and on toward Snowshoe is exposed, 

 within a distance of about ten miles, one of the most complete 

 and most accessible sections of Paleozoic rocks which can be 

 found anywhere in the State of Pennsylvania. It includes all 

 of the formations represented here from the base of the Beek- 

 mantown (Lower Ordovician) to the coal measures of the 

 Pennsylvanian (Upper Carboniferous). The lower part of this 

 section, consisting of the various members of the Ordovician, 

 has frequently been described and alluded to because it is one 

 of the most complete sections of this system which can be 

 found in the eastern part of North America. The object of 

 this paper, however, is to record a few observations on the 

 limestone beds which occur at the top of the next higher 

 (Silurian) system, and to correct a few errors which have crept 

 into the scanty descriptions of this region already in print. 



The region lies at the boundary between the last fold or 

 anticline of the Appalachian mountains and the front of the 

 Allegheny plateau. All formations in this vicinity outcrop in 

 a general north-east-southwest direction, parallel to the major 

 physical features. Nittany valley occupies the last eroded 

 anticline along the northwest side of the Appalachian moun- 

 tains ; the Bald Eagle ridge with its double crest is due to the 

 resistant, almost vertical beds of the Bald Eagle conglomerate 

 and Tuscarora sandstone on either side with the soft, easily 

 weathered Juniata red shale between them. These beds form 

 a part of the steeply dipping northwest limb of the JNittauy 

 valley anticline. Between the Bald Eagle ridge and the Alle- 

 gheny front is the long narrow Bald Eagle valley underlain by 

 Silurian and Devonian rocks. 



The Silurian beds are well exposed along the railroad track 

 from Milesburg gap, about one mile north of Bellefonte, 

 almost to the railroad bridge across Bald Eagle creek at Cen- 

 tral City. This bridge rests upon typical Oriskany sandstone 

 containing the characteristic Oriskany fossils in great abun- 

 dance. The northwest slope of Bald Eagle ridge is underlain 

 by a shale which has generally been referred to the Clinton. 

 Between this horizon and the Oriskany sandstone come two 

 distinct limestone beds separated by a considerable thickness 

 of shale. These two limestones are the subject of the present 

 discussion. 



