440 J. L. Campbell— Geology of Virginia. 
dip in the heavy beds of sandstone as they rise toward 
the crests of the ridges, are, however, common throughout the 
whole range. The limited irregularities may, with much plau- 
sibility, be referred to the undermining action of the river; 
for there are abundant indications that the water once st 
affected by heat throughout. Its position, too, has protected it 
against the erosive action of the river which has been far less 
here than it has been among the slates higher up in the series. 
Number 2 is a heavy mass of sandstone fully 350 feet thick, 
and so hard that we may call it “quartzite.” It consists of 
three tolerably distinct beds varying in hardness and color; the 
lowest being very hard and of a light gray, sometimes pinkis 
color; the middle one of coarser texture, partly conglomerate 
and mostly of a greenish gray color; the upper bed is more 
brittle than either of the other two, and of darker color. These 
heavy beds of hard sandstone seem to have presented one of 
was constructed the steep rugged outcrop of this massive ledge 
projected considerably over the left margin of the river, and 
‘Balcony Rock”—hence the name of the falls. 
etre 3. 
Number 3 consists of two heavy beds of slates separated by 
stratum of hard conglomeritic sandstone about sixty feet 
