552 C. SCHUCHERT SILURIAN FORMATIONS 



conglomerate of vein quartz, quartzite, schist, and serpentine, in the 

 main from the Precambrian strata to the eastward and in part from 

 the sandstones of the Bald Eagle below. There are no limestone 

 pebbles present. This conglomerate formation may also be of early 

 Richniondian age. 



Lorraine or Bald Eagle formation. Total thickness, 1,250 feet. Includes 

 the "Oneida Graj r sandstone" and Hudson River sandstones and shales 

 of Dewees, At the bottom the marine "Hudson River" begins with 

 dark greenish shales, that terminate in the upper 50 feet in thin strata 

 of blue ferruginous arenaceous limestones (182 feet thick). In these 

 limestones occur columnals of "Heterocrinus hetcrodactylus" Hall. 

 Trepostomata Bryozoa, Plectamhonitcs sericetls, Rafinesquina alter- 

 nata, Dalmanclla meeki, Orthorhyncula linncyi, Zygospira modesta, 

 Modiolopsis, Whiteavcsia, Byssonychia radiata (small here), and 

 Sinuites Mlobatus. These sandy shales pass into light greenish, fine- 

 grained sandstones and shales (330 feet) that are probably still of 

 marine origin, though they appear to be devoid of fossils, and then 

 into coarser-grained flaggy sandstones with fewer and fewer shale 

 partings (425 feet). Without break these are continued into the 

 "Oneida Gray" quartzites (313 feet), which become more and more 

 gray in color and conglomeratic (of well-rounded vein quartz pebbles 

 less than half an inch in diameter), cross-bedded and apparently 

 wholly of fluviatile origin, and pass unbroken into the Bald Eagle 

 formation that is wholly of continental origin. The section continues 

 downward unbroken into the still older Martinsburg formation. 



Tyrone Gap, Bald Eagle Mountain, Pennsylvania. — Twenty-five miles 

 west of Jacks Mountain. Based on a personal visit in June, 1916, and 

 F. Piatt: Second Geological Survey of Pennsylvania, Eeport T, 1881, 

 pages 16-18; Lesley: Final Eeport, volume I, 1892, 657-659; Grabau: 

 Bulletin of the Geological Society of America, volume 24, 1913, page 435. 



Devonian. 



Oriskany sandstone, about 50 feet. Coarse-grained sandstone in part con- 

 glomeratic. Not well exposed in this region. Best seen 27 miles 

 northeast at Milesburg. 

 Milesburg formation, or Lower Oriskany, about 130 feet. Thin-bedded 

 siliceous limestones, dark blue to black in color, terminating below in 

 black siliceous shales. The equivalent of the Shriver formation of 

 Maryland. 



Great break. All of Upper Helderbergian absent. 



Devonian. Helderbergian series. 



Keyser formation, or Lower Helderbergian, about 115 feet. To be seen in 

 northern and northwestern parts of Tyrone City. At the^»ase is the 

 cystid member, and toward the top occur two main zones of Stro- 

 matopora reefs. 



Possible hiatus at this level. 



