STRUCTURAL FEATURES IN THE FOOT-HILL REGION. 258 
series, of the beds last laid down, including the Creamy 
sandstone and at least one or two hundred feet of the beds 
beneath. The linear extent of the disappearance of the 
Creamy sandstone is probably somewhat under one mile, 
and is chiefly confined to the region immediately north of 
Clear creek, reaching to the south of it but slightly, if at all. 
In this interval the clays of the Fox Hills are found in close 
proximity to the Red Beds, the former conformable in strike 
with the Laramie sandstones above, the latter pursuing their 
usual trend, approximately parallel with the base of the range. 
The upper member of the Trias presents nothing anom¬ 
alous in its occurrence until within a distance of about two 
miles north and south of Clear creek, when a rapid dis¬ 
appearance of its beds successively from top downward is 
found to occur as the center of the region is approached, the 
limestones and associated beds at its base apparently reach¬ 
ing within a short distance of the limits already assigned for 
the Creamy sandstones below. An extremely important 
point in this connection is the fact that this disappearance 
occurs while the overlying Jura is not only still present, but 
maintains even the greater part of its thickness ; it occurs, 
in fact, between the Jura above and the lower member of the 
Trias, the Red Beds, beneath. The disappearance of this 
series of strata is most marked, because more sudden, to the 
north of Clear creek and Gold run, where within a distance 
of between a half and three-quarters of a mile it has decreased 
in thickness from 650 to 270 feet. The diminution in thick¬ 
ness to the south of Clear creek is also rapid, but over this 
portion of the region the upper Triassic member is not 
limited altogether by the Jura above, but in part by the 
Dakota, with a discrepancy of at least 10° in their strike. 
Farther to the south, where the Jura is present in nearly its 
full thickness, the variation in thickness of the Upper Trias 
is more gradual, but still to be associated with the local 
phenomena of the region. 
The Jura .—No extraordinary discrepancy in strike or in 
general relations between this formation and either the under- 
