2o6 GEORGE W. STOSE 



of the soluble cement to yellowish quartz sand, which is quarried 

 for building purposes. This bed also contains numerous Scolithus 

 linearis borings, and in places Camarella minor and fragments of 

 Olenellus^ have been found, by which its age has been determined 

 to be Georgian (Lower Cambrian). 



In the Catoctin and South Mountains of Maryland Keith has 

 mapped above the Weverton sandstone 800 to 1,200 feet of shale 

 (Harpers), and 500 to 700 feet of sandstone (Antietam). The Harpers 

 shale is typically exposed at Harpers Ferry, on the Potomac River, 

 and, as described by Keith, ^ consists of a bluish-gray shale with a 

 few thin sandstone beds. Northward these sandstones beds are 

 said to thicken, some attaining '50 feet, but do not have an appre- 

 ciable effect on the topography. On the road from Monterey to 

 Waynesboro, in the southeast corner of the area shown on the map, 

 this series is fairly well exposed, but, according to Keith, the struc- 

 ture is compHcated by folding and faulting. Above the Weverton 

 sandstone in this section, as seen by the writer, are shales or slates, 

 in part dark-banded, containing a conspicuous white, Scolithus- 

 bearing sandstone 20 to 30 feet thick, all of which is mapped by 

 Keith as Harpers shale. Above the shale is the Scolithus sandstone 

 in which Walcott found Olenellus and Camarella minor, as noted 

 above, and which is mapped by Keith as Antietam sandstone. 



North of Little Antietam Creek there are two ridge-making 

 sandstones above the Weverton sandstone, one composing Sandy 

 Ridge and the other Curve Mountain, and between them is black- 

 banded slate with thin ferruginous sandstones. The upper bed 

 forming Curve Mountain is undoubtedly the Antietam sandstone, 

 and it is apparent that one of the sandstone beds in the Harpers 

 shale of Maryland increases in prominence northward, so that in 

 Pennsylvania it reaches such dimensions that it forms a distinct 

 ridge. The Harpers formation in this area therefore consists of 

 shales and soft sandstones, with a quartzitic member near the middle 

 which is here named the Montalto quartzite, from Montalto Moun- 

 tain. Northward the shale gradually thins, and the sandstone con- 

 tinues to expand until at the northern border of the area it occupies 



1 Walcott, Bulletin of the U. S. Geological Survey, No. 134, p. 25. 



2 Loc. cit., p. 308. 



