472 J. J. Stevenson— Geology of Galisteo Creek. 
Passing the eastern outcrop of the Laramie, one comes at 
once to a wide park, lying mostly on the south side of the Ar- 
royo San Cristobal and eroded amid the Colorado shales. The 
Fort Pierre sub-group occupies the western side of this park 
and, as usual, is much thicker than are the Niobrara and Fort 
concretions, and the succession of dark, gray and yellow shales 
with abundance of selenite crystals. The concretions, except 
(Cretaceous No. 2) are ill-exposed at the base of the Dakota 
mesa, which forms the eastern boundary of the park, south 
from the Arroyo. 
The Dakota is well exposed, the three provisional groups, 
which will be proposed in my report, being shown along the 
east wall of the park and consists of light gray and yellow sand- 
stones; the Middle Dakota consists of blue, white and red 
sandy to clayey shales, with a bed of limestone, a conglomerate 
of limestone and iron ore and streaks of gypsum; while the 
Lower Dakota, made up of gray and yellow sandstones like 
those of the Upper Dakota, reaches eastward and becomes the 
Bpper part of a great mesa, the southwest wall of the Pecos 
valley. 
The succession in the lower Galisteo area is absolutely clear, 
showing the Dakota, Fort Benton, Niobrara, Fort Pierre an 
_ Laramie groups in their proper order. All of these dip west- 
_ ward until perhaps eight miles below Galisteo, where the dip 
_ Is reversed so that the Laramie beds run out at sixteen miles 
_ below Galisteo and the Fort Pierre shales come again to the 
_ surface. Each of these groups is perfectly characterized and 
iffic ey encountered in the attempt to identify them. 
al features and the fossils are not materially different 
elsewhere in the same groups within 
