G. K. Gilbert— Outlet of Lake Bonneville. 345 
ue lake phenomena of the Bonneville epoch in Marsh 
alley. 
ta terrace. 
If Marsh Valley had really been filled by the lake, as Cache 
Valley was, there could be no difficulty in finding evidence of 
the fact. The water would have been eight or ten miles broad 
and 400 feet deep, and the waves raised by the wind on a bay 
of such dimensions would leave most conspicuous monuments 
of their force. Arms of Lake Bonneville two or three miles in 
Width and less than 100 feet in depth have elsewhere been 
traced out by means of their distinct’ and well-characterized 
Shore lines, and this under conditions of slope, etc., similar to . 
those existing in Marsh Valley. 
Butif Marsh Valley contained no lake, of what nature are 
the terraces adduced by Dr. Peale in support of his concla- 
sions? The question is easier proposed than answered, but I 
think a partial explanation can be given. 
The first locality he mentions is “two miles north of Red 
Rock Pass, on the east side of the valley.” At this place there 
18 @ conspicuous stream terrace at about the right altitude to 
personate a delta terrace of the Bonneville series. Its surface 
Is part of an alluvial cone formed by Marsh Creek before the 
Bonneville epoch, and its searp is one wall of the channel worn 
by the outflowing river during that epoch. The river pared 
away the margin of the sloping plain spread by the creek and 
left the remainder as a terrace. The edge of this terrace jis, at 
its highest point, 50 feet higher than the nearest trace of the 
Bonneville beach, two miles away ; and it descends northward 
* 
