MORRISON SHALES OF COLORADO AND NEW MEXICO 43 
photograph, where the third detailed section was taken. The 
cap rock of the butte is the Exeter formation, to be described 
beyond. In this region it immediately underlies the shales in 
place of the gypsum which is absent. No detailed section was 
taken east of this point, but the outcropping edges of the forma- 
tions were seen continuously in the canyon sides to a point about 
seven miles east of the eastern boundary of New Mexico, where 
the eastward dip of the strata carries the shales beneath the 
canyon bottom. 
In the section east of Exeter, the Dakota rests upon a series 
of variegated clay shales which contain layers of sandstone and 
impure limestone, and at this point the limestone attains greater 
importance than at other places examined in the Rio Cimarron. 
The brown limestone near the base resists erosion to such an 
extent that a shelf often several rods wide is produced in the 
canyon side. In the concretionary limestone near the top was 
found the only invertebrate fossil obtained from the shale 
formation of the Rio Cimarron. It is a fragment of a pele- 
cypod too poorly preserved to identify. 
The formations represented in the detailed sections, with the 
exception of the Exeter formation, to be described later, were 
traced continuously from Folsom eastward to a point seven 
miles beyond the boundary of New Mexico. The canyon sides 
are steep and well exposed throughout this distance and no 
difficulty is encountered in following the outcrops. Throughout 
this distance the Dakota sandstone forms the protecting rim of 
the canyon walls, while the middle portions of the walls are as 
uniformly occupied by the shale formation. This middle forma- 
tion consists mainly of clay shales of various colors, and friable 
sandstones, varying from nearly pure silica to various admixtures 
of clay and sand. In certain places, however, the sandstones 
are hard, coarse, and slightly cross-bedded. The character of 
the formation varies laterally within short distances. The lime- 
stone which forms a subordinate amount of the formation, may 
occur at any horizon. The layers are generally less than one 
foot thick, and never, so far as observed, attain a thickness of 
