468 The American Naturalist. [May, 
1. The Wasatch mountain range is carved from a large block of 
crustal material, uplifted along a fault plane at one side. The block 
adjoining the fault plane on the opposite side is thrown down. Erosion 
s continually transferring material from the uplifted block to the down- 
thrown block, and there is direct evidence that the mountain is steadily 
rising or the valley sinking, or both. Some advocates of the isostatic 
theory would regard this progressive relative displacement as a direct 
effect of the continual transfer of load. Under this view the moun- 
tain block has less density than the valley block, and the two are in 
isostatic equilibrium ; the unloading of the mountain block by erosion 
and the loading of the valley block by deposition disturb the equi- 
librium, and it is restored by vertical movement on the fault plane. 
An arm of Lake Bonneville occupied the valley, filling it to an 
average depth of 500 or 600 feet, and this load of water was somewhat 
quickly added and afterward somewhat quickly removed. If the valley 
block were delicately sensitive to the application of load, it should be 
depressed about 200 feet by the access of water, and should rise a 
corresponding amount when the water was removed. But this did not 
occur. On the contrary, the depression of the valley, as shown by 
changes occurring along the fault plane, continued alike during the 
presence of the water and after its removal. It is therefore concluded 
that the local transfer of load from one orognic block to the other is 
not the primary cause of the progressive rise of the mountain and 
depression of the valley, and the question arises whether the mountain 
range may not be wholly sustained in virtue of rigidity. 
2. Considering the main body of Lake Bonneville, it appears from 
a study of the shorelines that the removal of the water was accompa- 
nied, or accompanied and followed, by the uprising of the central part 
of the basin. The coincidence of the phenomena may have been 
fortuitous, or the unloading may have been the cause of the uprising. 
Postulating the casual relation, and assuming that isostatic equilibrium, 
disturbed by the removal of the water, was restored by viscous flow of 
crust matter, then it appears (from the observational data?) that the 
flow was not quantitatively sufficient to Satisfy the stresses created by 
the unloading. A stress residium was left to be taken up by rigidity, 
and the measure of this residium is equivalent to the weight of from 
400 to 600 cubic miles of rock. 
From these phenomena and theoretic considerations arises the 
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3 $ £011 g : : i 
5 © not y yp : pp on Lake Bonne- 
ville now in press, constituting Vol.I. of the Monographs of the U.S. Geological Survey. 

