BONNEVILLE FAULTING 
145 
level a thousand feet this pressure was of course relieved. In 
the concompitant lowering of the delta watertable the latter succes¬ 
sively reached slopes which formed glidding planes and permitted 
the main masses of incoherent delta materials to slip measurably. 
Gilbert emphasizes the fact of the recency of these delta faults, 
so near to us in time that their scarps are still often unweathered. 
He is probably wrong in inferring that these were the only faults. 
Between the Bonneville Lake epoch and the present time there 
must have occurred repeated, if not more or less continuous, slip¬ 
ping, which stream-action, storm-wash, and weathering effects 
generally during this long interval united in destroying complete¬ 
ly all evidences of movement except the very latest, perhaps all 
except those which occurred since the occupation of the region by 
civilized man. 
It would be instructive if instrumental surveys could be made 
to determine the exact amounts of delta sinking that has taken 
place since the high-stage of Bonneville waters as indicated by 
the uppermost sea-cliffs cut in the hard rocks of the mountain 
faces. With the factors of original delta slope, the exact position 
of the strand-line, and subsequent disastrophic movements, this 
determination might be a task both delicate and complicated; but 
it does not seem to be an impossible one. It would well be worth 
the effort expended. 
In using the delta faults to support his Basin Range hypothesis 
Gilbert unwittingly furnishes not only the strongest possible argu¬ 
ment against his theory, but he renders quite negatory the Dutton- 
ian hypothesis of isostasy. Now a fundamental premise of both 
the Gilbertian and Duttonian hypotheses in orogeny is that the 
fault should have small hade. But in Gilbert’s diagrammatic 
analysis of the delta faults, as secondary expressions of the master- 
fault of the Wasatch front, there is represented dislocation of high 
hade. Under such circumstances the rising of the mountains 
would be a physical impossibility. Nor does Willis’ recent sup¬ 
plementary hypothesis of a rotating orogenic block overcome the 
difficulty. Pushing the difficulty into the twilight background 
merely confuses the situation still the more. The same grave 
objection obtains in the case of Lauterback’s high-haded faults 
of the Humboldt Mountains. 
