342 G. K. Gilbert— Outlet of Lake Bonneville. 
Dr. Peale treats, in the same article, a question of priority 
and other matters of purely personal interest, and his re- 
marks thereon invite reply, but I have a strong distaste for 
personal controversy, and I am confident that the readers o 
the Journal—not even excepting Dr. Peale—will cheerfully 
excuse me if I refrain. I shall therefore confine myself to the 
The term terrace is applied in topography to a level surface, 
or one of very gentle slope, limited on one side by a suriace 
which descends at a greater angle, and usually limited on the 
other by a surface which ascends at a greater angle. here 
the limiting slope is steep it is called a scarp. A scarp ma 
stand above a terrace, rising from its inner edge and in 
toward it, or it may lie below it, falling from its outer edge an 
facing from it. Most terraces are margined by scarps on one 
edge or the other, and some on both. | 
Terraces are produced in at least five different ways, namely : 
by differential erosion, by streams, by waves, by differential 
deposition, and by displacement. : 
Terraces by Differential Erosion arise wherever a series of 
dissimilar strata lying nearly horizontal are subjected to rapid 
erosion. T t strata are destroyed more rapidly than the 
hard, and the latter, where they overlie soft beds, are under- 
mined so as to break off by vertical fracture. A stair-like 
system of terraces and scarps is thus formed, in which each 
terrace marks the outcrop of a soft rock and each scarp the 
outcrop of a hard one. 
These terraces are distinguished from all others by the con 
stant relation of form to stratigraphic structure. . 
tream terrace is produced whenever a stream, which has 
flowing at the upper level the water forms a broad flood plain. 
By the subsequent excavation this plain is in part destroyed, 
and what remains becomes a terrace. A scarp of even height 
separates the terrace from the new channel of the stream oF 
from a new flood plain. 
