ELISHA MITCHELL SCIENTIFIC SOCIETY 96 
which it joins. Further back from the Cape Fear the 
cutting down through alternate layers of loose sand and 
tough clay has resulted in producing a rapid but irregu- 
lar current with occasional small shoals, at several of 
which waterpowers have been developed by the construc- 
tion of dams and factories erected. 
Figure 2 may be considered as illustrating fairly well 
Fic. 2.—Conditions favoring ‘the develop- 
ment of cascades and rapids in stream beds 
crossing geologic contacts. 
g+=Granite and gneiss. sch—Crystalline 
schists, in which the harder places (shaded 
more heavily) wear away less rapidly than the 
intervening softer places. The result is a series 
of cascades and rapids in the stream. f= 
Coastal plain deposits—gravel, sand and loam. 
a generalized section across the fall 
line where crossed by the Roanoke 
river at Weldon. The crystalline 
schists exposed along the river bed 
between Gaston and Weldon (G and 
W of fig. 2) are much harder and 
more obdurate than the unconsoli- 
dated coastal plain deposits below, 
and even harder than the granite and 
oneissic rocks above it; and hence 
the latter rocks have been eroded to 
greater depths, and at the line of 
junction between the two (1 in fig. 2) 
the schists form a sort of barrier or 
natural dam, for many miles above 
which the river is deep and the cur- 
rent sluggish. But from this point 
FIG. 2. 
down to Weldon the schists vary in hardness, and are 
intersected by joints, seams, fissures and probably sev- 
