MORRISON SHALES OF COLORADO AND NEW MEXICO 45 
the shales of the Rio Cimarron, although ranchmen from that 
vicinity report having seen large petrified bones. A comparison 
of this formation, however, with the shale formation of the Pur- 
gatory, indicates that the two are identical in composition and 
stratigraphic position, and leaves little room for doubt that they 
are parts of one and the same formation. 
In the vicinity of Exeter post-office the shales are separated 
from the underlying Red Beds by a well-marked unconformity. 
The Red Beds were thrown into gentle undulations and these 
undulations eroded previous -to the deposition of the younger 
sediments upon them. Several miles west of Exeter post-office 
the shales rest upon the eroded edges of a local arch, from the 
top of which about sixty feet of the Red Beds had been removed 
previous to the deposition of the shales. The gypsum, which is 
here considered as the top of the Red Beds, appears in the flanks 
of the truncated arch. From this point eastward for several 
miles angular unconformities were noted at the top of the Red 
Beds. In the vicinity of Exeter, the thickness removed by ero- 
sion is considerable, but no attempt was made to estimate it. 
The dip of the truncated Red Beds may be estimated from the 
accompanying photograph (Fig. 4). 
Near Exeter post-office a sandstone formation appears 
between the Red Beds and the shales. It lies unconformably 
upon the Red Beds as shown in the illustration (Fig. 4). The 
cap rock of the butte at the left is this new formation, which I 
shall for the present call the Exeter sandstone. It is a firm, hard 
and rather coarse but evenly laminated sandstone, pink to white 
in color. The lower strata are pink, while those above grow 
progressively lighter colored. It has the appearance of being 
composed of the coarser material from the eroded Red Beds, 
and may be a basal sandstone formed by the encroaching waters 
from the east or south, which cut away the Red Beds. The 
sandstone has a maximum thickness of seventy-five feet, and 
extends froma point several miles west of Exeter, where it thins 
out, eastward to the New Mexico line where it drops beneath the 
canyon bottom. No fossils of any kind were found in this sand- 
