Bui. 348, U. S. Dept. of Agriculture. 
Plate VI 
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Fig. 1.— Granite. 
FlQ. 2.— Rhyolite. 
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Fig. 3.— Gabbro. 
Fig. 4— Diabase. 
Fig. 5— Sandstone. Fig. 6.— Schist. 
SCREENINGS FROM ROAD-MAKING ROCKS. 
