MORRISON SHALES OF COLORADO AND NEW MEXICO 51 
grounds. There is little doubt that the upper sandstone belongs 
to the Dakota. It is possible, however, that there may be some 
question regarding the lower limit of the Dakota. In the canyon 
of the Purgatory, the Dakota sandstone rests upon variegated 
shales which are in places full of Dinosaur bones. There can be 
Fic. 7.— The Canadian escarpment west of La Centa Canyon, N. M. The sum- 
mit is Dakota. The gentle shape near the top is occupied by the shales, with heavy 
sandstone at the base. The massive “columnar”? layer—too feet thick—is the 
upper part of the Red Beds —the possible Trias. The lower portion is occupied by the 
Red Beds (Permian). 
no doubt in this case as to where the line of separation should 
be drawn. The same change of character in passing from the 
Dakota to the shales obtains in the canyons of the Rio Cimarron 
and the Canadian. It is therefore probable that the lower limit 
of the Dakota is properly placed at the lower limit of the massive 
sandstone, and that the shale formation beneath is separate and 
distinct from the Dakota, although conformable with it. It is 
