120 SLATE DEPOSITS AND INDUSTRY OE UNITED STATES. 
or its tributary "runs," where the mass has been denuded of its weathered zone, it 
has a well-marked easterly dipping (exceptionally westerly) slaty cleavage crossing 
Scale of miles 
Contour interval 100 feet 
Fig. 15.— Map of slate region about Martinsburg, W. Va. (From Geologic 
Folio No. 10, Harpers Ferry, II. S. Geol. Survey.) Shading represents area 
underlain by Martinsburg shale. Slate quarry is shown by crossed hammers; 
slate prospects by round dots; strike of commercial slate by arrow. 
the bedding at various angles, and pieces, when struck with a hammer, give the 
typical ring of a slate. The slatiness of the formation is, however, inconstant, 
