54 CED AGE 
Ti, however, the sandstones were laid down against the base of these 
high cliffs, they should contain a coarse and abundant angular 
limestone conglomerate, whereas a careful search nowhere revealed 
any Madison limestone in any of the sandstone of the formation. 
This constitutes abundant evidence that the Fort Union(?) actu- 
ally passes beneath the fault block and does not lap against its foot. 
As to the second problem, the exact age and equivalence of the 
beds called Fort Union(?), a less definite conclusion is possible. 
They are younger than the Cody, upon which they rest with slight 
angular unconformity at places. The fact that they are involved 
in the major faulting and folding makes it probable that they are 
not Wasatch, as Hewett has suggested, since beds of that age are 
known to cover similar major faults in Idaho.t The only other 
formations with which it seems at all possible to correlate them are 
Hewett’s Gebo (Fisher’s basal Laramie) or Hewett’s Fort Union( ?) 
(Fisher’s upper Laramie), and to the writer the evidence seems in 
favor of the latter conclusion. If these beds are the equivalent 
of Hewett’s Fort Union, it still remains to determine whether | 
they represent the equivalent of the original Fort Union and 
whether they are very late Cretaceous or early Tertiary, problems 
with which this paper has nothing to do. 
These faults involving the Fort Union(?) pass at many points 
beneath the Andesite, which Hague, in the Absaroka Folio, has 
called the Early Basic Breccia and which he considers to be of 
early Neocene age. This would date the faulting as taking place 
after the sedimentation of the Fort Union(?) and before the 
Neocene, probably in very early Tertiary time, since following the 
faulting long erosion had trenched the region deeply and in places 
completely cut away the fault block, before the Basic Breccia was 
laid down. 
CORRELATION WITH OTHER FAULTS 
Richards and Mansfield? have presented a concise statement of 
the available information regarding major thrusts in the northern 
Rocky Mountains, and hazard a possibility that these may consti- 
tR. W. Richards and G. R. Mansfield, ‘‘The Bannock Overthrust,” Jo. Geol., 
XX (1912), 704. 
2 Op. cit. 
