THE SHENANDOAH LIMESTONE AND MARTINS- 

 BURG SHALE 1 



INTRODUCTION 



While engaged in fieldwork on the Maryland Geological 

 Survey, the writer has had an opportunity to examine to some 

 extent the upper part of the Shenandoah limestone and the over- 

 lying Martinsburg shales. 



Shenandoah limestone. — The name Shenandoah was proposed 

 by Mr. Darton in 1892 for the limestones of the Shenandoah 

 Valley and the formation was described in the vicinity of Staun- 

 ton, Va., as consisting of "a great mass of impure magnesian 

 limestones below, grading upwards through a series of cherty 

 beds of no great thickness into several hundred feet of light- 

 colored, heavily bedded purer limestones. The lower beds were 

 not found to be fossiliferous. In the cherty beds only a few 



middle Ordovician gasteropods were found The upper 



member is sparingly fossiliferous at many localities with a mid- 

 dle to upper Ordovician fauna in which the forms Orthis Occident- 

 alls, 0. testudinaria, Leptcena alternata, and Chcetetes lycoperdon were 

 predominant. Pleurotomaria subconica, Conularia trentonensis , Platy- 

 notus trentonensis, and several others were also noted." 2 



Mr. Darton in his account of this formation in the Staunton 

 folio described an upper member of the limestone from 200 to 350 

 feet in thickness which is said to be purer, more thickly bedded 

 and generally of lighter color than the older part of the forma- 

 tion. It is also stated that in the upper division "fossils occur 

 also in greater or less profusion throughout its course. The 

 fauna is that of the Trenton limestones of New York." 3 



Martinsburg is near the northwestern corner of the Harper's 

 Ferry sheet which was mapped by Mr. Arthur Keith, 4 and the 



1 Published by permission of Dr. Wm. Bullock Clark, State Geologist of Maryland. 



2 Amer. Geo!., Vol. X, p. 13. 3 Geologic Atlas of the U. S., Folio 14, 1894, p. 2. 

 4 Geologic Atlas of the U. S., Folio 10, 1894. 



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