414 WILBUR C. KNIGHT 
incline, from either side, unchanged rocks belonging to the Carboniferous, 
Triassic, Jurassic, Cretaceous, and in some localities Tertiary. 
In both of these references Hayden took it for granted that 
the Red Beds were Triassic. 
The next important geological contribution to science in 
reference to the Laramie Plains Beds appears in the Systematic 
Geological Report of the Fortieth Parallel Survey, under the heading 
of ‘‘Triassic,’’ pp. 249, 250, which reads as follows: 
Directly overlying the Palaeozoic limestones, in conformable superposi- 
tion, and not infrequently overlapping the Palaeozoic, and coming directly 
into nonconformable contact with the Archean, appear the well-known Rocky 
Mountain Red Beds, which, from their position between the Coal-measures 
below and the well-recognized Jurassic beds above, have been generally 
assigned to the Triassic age. Reserving all discussion of the validity of this 
assignment to later pages of this chapter, it is proposed here to give simply a 
brief statement of their physical condition and continuity along the flanks of 
Colorado Range within the field of this exploration. From the lower limit 
of the map nearly up to the forty-first parallel, the Red Beds lie directly upon 
the Archean, and form, with soft, friable strata, a remarkable contrast with 
the adjoining crystalline rocks, the red series varying in thickness from 300 
to 850 feet. It is interesting to observe that where they are in direct contact 
with the Archean rocks they have a dip rarely exceeding 15 degrees, and 
often retaining an approximation to the horizontal; while to the north, where 
erosion has been deep enough to reach and uncover the Paleozoic series, the 
dip increases to the vertical, with exceptional instances of slightly reversed 
position. The region of contact between the Trias and the Archean affords 
an interesting display of the mode of deposition of the coarse, friable gravel 
and sandy material of the Trias upon the hard irregularities of the crystalline 
series. 
In the same chapter, pages 256-58, King refers to the Red 
Beds in the southern portion of the Laramie Plains as follows: 
South of the railroad on the western side the contact of the Trias with 
the Archean is rather interesting. It is seen gradually to overlap the gentle 
inclinations in thin beds, and to abut squarely against the steeper slopes of the 
Archean. In general, it dips gently away from the Archean, the Trias ridges 
being defined by the harder beds which have protected from erosion the 
softer and more shaly portions below; and wherever there are lines of erosion 
parallel to the contact-line with the Archean, the steeper or more escarped 
faces are turned toward the range. 
Gypsum deposits are well shown north of the Willow Creek and the 
