G. K. Gilbert— Outlet of Lake Bonneville. 343 
It is characteristic of stream terraces that they slope in the 
direction of the stream that carved them. 
ave terraces are found on the shores of all bodies of 
water. The action of waves, combined with that of currents, 
carves away the land on all salients. The direct action is con- 
fined to a few feet above and below the water-level, but what- 
ever is undermined by the waves is thrown down by gravit 
and brought within their reach. The results of the erosion 
are, first, a broad terrace lying under shallow water and sloping 
gently from the shore; and, second, a sea-cliff or scarp spring- 
ing from the water’s edge. 
It is one of the chief characteristics of a wave terrace that 
of the detritus it transports is deposited at its mouth, 
he effect of this is to extend its bed on the side toward the 
deep water. As the mouth protrudes a deposition takes place 
along the bed, so as to maintain a constant declivity of chan- 
nel, and soon the bed is so raised that the water finds a lower 
way at one side and leaves it. By a repetition of this process 
the mouth of the stream is shifted from point to point, and the 
delta is made to encroach on the lake along its whole face. 
he form eventually produced is that of a terrace sloping 
gently down to the shore and there limited by a submerged 
ot The declivity of the scarp depends on the coarseness 
of the material deposited. The declivity of the terrace is 
identical with that of the stream which formed it. The con- 
tour separating the terrace from the scarp is a curve convex 
toward the lake. 
A chief characteristic of a delta terrace is that its lower 
edge, where it joins the scarp, follows a water line and is hori- 
zontal. In the delta terraces of Lake Bonneville the horizon- 
tality remains though the water has disappeared. 
erraces displacement are usually produced by faulting. 
rates the two by a scarp. The scarp is the only feature added 
to the Pa a ig ari its addition the raised portion of the 
slope becomes a terrace. 
hatever is characteristic of the terrace by displacement 
ertains to the scarp. A fault scarp usually holds an even 
eight for long distances. It maintains an even, often a 
