SEDIMENTARY ROCKS OF SOUTH MOUNTAIN 209 



Stones, fragments of trilobites and other fossils suggesting Acadian 

 (Middle Cambrian) age, were found by the writer. The sandstone 

 and the purple shale also outcrop conspicuously in the ridge just 

 north of Waynesboro, so the name "Waynesboro formation" is 

 suggested for this division of the Shenandoah. In central Vir- 

 ginia H. D. CampbelP recently subdivided the Shenandoah limestone 

 into several formations, separating at the base a limestone and an 

 overlying series of variegated shale, which he named respectively the 

 Sherwood limestone and the Buena Vista shale. Presumably these are 

 the same subdivisions mapped in this area, but from the data at 

 hand this can not be determined for certain, and since it is known 

 that a large fault and corresponding gap in the stratigraphy occur 

 in the intervening Harpers Ferry area, new names arc here proposed 

 for the formations. 



Massive, bluish-gray, magnesian limestones, with numerous 

 thin layers and nodules of chert and beds of shale, possibly 2,000 

 feet in all, compose the next formation. Red and green shales 

 are present in the middle of the formation, and beds of sandy hme- 

 stone, which in places form low ridges, occur higher in the section; 

 but none of the beds have been traced for any considerable distance. 

 The only fossils which have been found in this portion of the section 

 are those mentioned as occurring in the basal layers and indicating 

 Acadian age. The name "Elbrook limestone," from a town at 

 which the formation is quarried, is proposed. 



A change to siliceous sediments with conglomerate, oolite, and 

 red clay, marks the base of the next succeeding formation. The 

 sihceous layers weather to granular porous sandstone, which pro- 

 duces a low ridge and offers another marker in the otherwise uniform 

 limestone section. Conglomerates of rounded pebbles of dense 

 magnesian Hmestone, imbedded in a matrix largely of quartz grains, 

 indicate an elevation of a portion of the nearby sea bottom into 

 a land area and the erosion of the Hmestone, the quartz sand coming 

 from a more distant source on the land. Other conglomerates 

 or breccias of flat fragments of thin slabby Hmestone variously 

 arranged in a matrix of calcareous mud are intraformational con- 

 glomerates derived from recently deposited silt broken up by wave, 



I American Journal of Science, Fourth Series, Vol. XX, No. 120, pp. 445-47. 



