68 
SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
the northern corner of the District of Columbia. Its important features are these: 
Sugarloaf Mountain is a mass of eastward-dipping Cambrian sandstone passing 
toward the east into and under a belt of slaty or schistose rocks (phyllites), which 
Contour interval 50 feet 
Fig. 5.— Map of parts of Frederick and Montgomery counties, Maryland, showing (by dots) slate pros | 
pects and abandoned quarries. 
Williams described as containing sericite, chlorite, quartz, hematite, and tourmaline | 
The phyllite area is traversed in several places by Mesozoic diabase dikes, and eas' 
of it are contorted gneisses. 
