THE OLDER MESOZOIC OF ARIZONA. 27 



beginning as mortar beds, such as I have described, but soon taking on 

 more symmetrical forms, closely resembling the marl buttes of the valley 

 below. The color also changes, and many of the buttes are, in whole or 

 in part, of a deep blue or a lively purple. These constitute here the highest 

 beds of the Shinarump, and fossil wood is abundant throughout. Much 

 the same conditions prevail in the Petrified Forest region, but the develop- 

 ment is here much less extensive. 



THE PAINTED DESERT FORMATION. 



It remains to consider the third and highest formation of the Older 

 Mesozoic of Arizona. As already stated, these constitute the elevated 

 cliffs that bound the valley of the Little Colorado on the northeast. 

 Although broken through in many places, and practically wanting 

 for long distances, they constitute what may be regarded as a great 

 wall, separating the valley from the region of high mesas that lie in 

 the Moqui and Navajo country. As these beds seem to contain no 

 fossil remains, and as they are throughout the greater part of their 

 extent practically inaccessible because of the absence of water, their 

 detailed study has been neglected, and I was able to acquaint myself 

 with them only imperfectly and at a few points. 



There is, however, no place where they are better developed than 

 directly east of Tanners Crossing, where we remained longest, and on 

 several occasions the attempt was made to reach them from our camp 

 and to examine them closely. Enough was learned to justify the posi- 

 tive statement that they consist almost entirely of sandstones, per- 

 fectly stratified, the different layers differing mainly in color, thickness, 

 and fineness of structure. The great central portion constituting the 

 escarpment and having a thickness of about 800 feet is, within these 

 limitations, practically homogeneous. The series begins, however, with 

 a bed of orange-red sandstone, highly argillaceous, and soft in structure, 

 easily eroded, and readily yielding to the influence of wind. It has a 

 thickness of about 100 feet, and in the lower Colorado region stretches 

 across the broad valley at the base of the escarpment and lies directly 

 upon the uppermost limestones of the Shinarump. Here it forms pic- 

 turesque and fantastic buttes and chimneys standing out upon the 

 plain. It occurs in the same position overlying the Shinarump on 

 Lerovix Wash and forming the top of the mesa which overlooks the 



