160 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
They have recognized its completeness farther south, but conclude 
that in the Virgin River district the baselevelhng was not so perfect, 
since "the hiva after crossing tlie fauk was soon checked by an escarp- 
ment of hmestone rising two or three hundred feet with a fairly strong 
slope" (Huntington and Goldthwait, '04, p. 230). We have seen, 
however, that the lava here referred to was the recent flow which 
followed the second faulting movement, and that the "escarpment" 
was the one produced by this second faulting, and not one left after 
the baselevelhng period. At the close of that period, the scarp formed 
by the first faulting was probably as completely obliterated here as 
elsewhere, the position of the baselevel surface being possibly 1,000 
feet higher than the surface covered by the lava flow exposed at the 
crossing of the Virgin. It apj')ears that this same confusion occurs in 
the authors' interj^retation of the fault north of Toquerville, as 
three movements instead of two are indicated by the topography along 
that portion of the fault. 
According to our observations the Hurricane Clitfs in the Mrgin 
River district are wholly the result of recent faulting, and represent 
two difl^erent movements separated from each other by an erosion 
period, and from the first faulting by a long baselevelhng period. 
Summary. 
South of the Canon, in the San Francisco Plateau, displacements 
are more numerous than has been supposed, although of little im- 
portance compared with the great displacements north of the Canon. 
The "crags" of the Echo Clift's probably owe their peculiar form to 
erosion guided by strongly marked crossbedding, and possibly in part 
also to the influence of a well developed system of joints. The Sevier 
and Toroweap Faults are independent and do not join each other to 
form one great displacement, as has been thought might be the case. 
The Hurricane Clift's in the vicinity of the Virgin River are true fault 
cliff's wholly due to recent faulting at two different periods. In all, 
three periods of faulting along the same plane have occurred in that 
region, the first and second periods being se]:)arated from each other by 
a long era of baselevelling, while the second and third periods were 
separated by a shorter, but none the less distinct, erosion interval. 
Observations made along other displacements in the Grand Caiion 
district confirm the theory that the faults of this district are in the main 
of ancient date. 
