656 CHARLES S. PROSSER 



line between the Shenandoah limestone and the Martinsburg 

 shale is clearly shown in the vicinity of that city, but the descrip- 

 tion of the formation gives no additional information regarding 

 its age. 



Professor Wm. B. Rogers considered that tlie Trenton, Utica 

 and Hudson River formations were represented in the Potomac 

 Valley at Williamsport and to the west ; but he apparently 

 regarded the greater part of the limestone as of Chazy, Levis 

 and Calciferous age. 1 



Martinsburg Shale. — The name Martinsburg shale, like that 

 of the Shenandoah limestone, was proposed by Mr. Darton from 

 the exposures near Martinsburg, W. Va., "a region in which," 

 he states, "the formation is extensively and typically exposed." 

 It is stated that at the base there is "a thin series of alternating 

 thin bedded limestones and slates " but for the most part the 

 rocks of the formation "are slates and shales, mainly of dark 



color The beds are fossiliferous at many points ; grapto- 



lites are found in the basel beds, notably in some light colored 

 weathered shales in cuts of the Chesapeake and Ohio Railway, two 

 miles east of Staunton and further east ; along the Little North 

 Mountain, and in the Warm Spring, Crab Bottom and other anti- 

 clinal valleys westward, remains of upper Ordovician brachiopoda 

 are moderately abundant. The forms most frequently met with 

 are Leptcena sericea, L. altemata, Orthis testudinaria, 0. pectinella, 

 and Modiolopsis modiolaria. The precise equivalency of the for- 

 mation is not known, but judging from its general relations and 

 fauna it probably comprises the Utica, Hudson River and possi- 

 bly small amounts of adjacent formations of the New York series. 

 It is the No. Ill of Rogers' reports and has generally been 

 called ' Hudson River.' " 2 



Under the description of the formation in the Staunton Folio 

 Mr. Darton states that "In the Jack Mountain exposures fossils 

 are abundant, and the species are of Hudson age," while " In the 



1 See Plate No. VII, Sec. No. 1, in " A Reprint of Annual Reports and other papers 

 of the Geology of the Virginias," edited by Jed. Hotchkiss, 1884. 

 2 Amer. Geol., Vol. X, pp. 13, 14. 



