TIIK OLDKK MKSOZOIC OF AinZONA. 27 



l)eo;innin<; as mortar beds, such as T liavo dcsciilxMl. Init soon takino; on 

 more synnnetrical forms, closf^ly resemhliiisi the mai'l hiitles of the valley 

 helow. The coloi' also changes, and many of the t)utt(>s ar(\ in whole oi' 

 in part , of a dec^p hlne or a hxcly pur])le. These constitute here the hi^i'liest 

 \hh\s (if tlie ShiiK-ii'um]), and fossil wood is al)undaut thi'ou.iihout. Much 

 th(> same coudil ions j)re\'ail in tlie PetriHed I'Orest refiiou, hut tluMlevelop- 

 ment is ]i(>re much less extensive. 



77/ A' I'AlXTh'D DESEltr l-OHM ATIOS . 



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

 Mesozoic of Arizona. As already stated, these constitut(> th(» (devated 

 cliffs that hound the valley of the Little Colorado on tiie northeast. 

 Although broken through in man>' places, and practically wanting 

 for long distances, they constitute what may l)e regarded as a great 

 wall, sepai'ating the valley from the region of high mesas that lie in 

 the Moqui and Navajo coimtry. As these l;)eds seem to contain no 

 fossil remains, and as they are throughout the gi'eater {)art of tlieii- 

 extent practically inaccessible l)ecause of the aljsence of water, their 

 detailed study has been neglected, and I was able to actjuaint myscdf 

 with them onl}' imperfectly and at a few points. 



There is, however, no place where they are better develo})ed than 

 directly east of Tanners Crossing, whei'e we remained longest, and on 

 several occasions the attempt was made to reach them fi'om oui- camp 

 and to examine them closely. Enough was learned to justify the j)osi- 

 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 l)egins, however, with 

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

 easily eroded, and I'eadily yielding to the influence of wind. It has a 

 thickness of about 100 feet, and in the lower Colorado i-egion stretches 

 across the bi'oad valley at the base of the escarpment and lies du-ectly 

 upon the upp(>rmost limestones of the Shinarump. Here it forms pic- 

 turesque and fantastic l)uttes and chimneys standing out upon the 

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

 Leroux AVash and foi'ming the top of the mesa which ovei'looks the 



