18 
THE EOCENE PLATEAU. 
where some large tree had broken up. At one point east of the river, I 
found the stump of a dicotyledonous tree which measured five feet in diameter. 
As already remarked, the Puerco marls may belong to the Eocene 
series in view of their strict conformability to the superincumbent rocks of 
that age. But they may represent the Fort Union or lignite beds of the 
Upper Missouri, some of whose strata they resemble in color and consist¬ 
ence. They contain no lignite nor coal, although their occasional black 
color may be due to a small amount of carbonaceous matter. They have 
no resemblance to the Bitter Creek beds in mineral character or fossils. 
The presence of such quantities of petrified wood gives weight to the 
probability that the Puerco marls are a lacustrine formation. In explor¬ 
ing the hills of this formation along the Puerco, I found the horns of 
an Elk {Cervus canadensis). This locality must be near the southern limit 
of its range. I learned that it is not uncommon on the high* plateau near 
Tierra Amarilla on the northeast. 
I made a second section of the upper or Wahsatch beds to the west, 
starting from opposite the middle of the northern bad-land cove. About 
the middle of the marl series, there is usually present a bed of nearly white 
sandstone, frequently quite hard, in which the fossils have generally a worn 
or rolled appearance. Here occurred the greater number of Sharks’ teeth, 
but not all. Above this horizon, the most abundant fossils are the gars and 
crocodiles, while the greater number of the Mammals come from below it; 
but this distinction is of a very general character. On climbing the eastern 
escarpment of these marls, the summit is found to be a plain sloping at a 
slight angle to the south and west. Escarpments composed of the upper 
beds of marl and sandstones extend mostly in east and west lines. 
The most imj)ortant of these is, first, an outcrop of sandstone, ten 
miles west of the bluffs. Here I found characteristic fossils. The trail fol¬ 
lows a Canada, or narrow shallow valley, for perhaps forty miles. Branches 
pass to the right and left between the hills, affording beautiful park-like 
views. The drainage of this Eocene plateau from the summits of its eastern 
escarpment is to the west, reaching the San Juan Piver by Canon Largo 
and Canon Amarillo. Along the Canada, the marls re-appear; their red 
and gray colors contrasting with alternating beds of sandstone. These 
