28 MESOZOIC FLORAS OF UNITED STATES. 



amphitheater that I have described. It is also seen above the Shina- 

 rump to the east of the Petrified Forest. It is therefore probably safe 

 to assume that this formation is continuous from Echo Cliffs to the 

 boundary line of New Mexico. 



Of the painted cliffs there seems to be httle more to say. In 

 looking at these cliffs from a distance it is seen that they are overlain 

 by a white formation, the nature of which it is important to consider. 

 Before we had visited the region, so as to obtain a close view of them, 

 it was natural to suppose that they might constitute Jurassic limestones 

 and that the Triassic system might terminate at the line which separates 

 them from the variegated sandstones. But upon close examination 

 this was found not to be the case, and these white rocks were found to 

 consist of sandstones, often ver^- pure and cross-bedded, with scarcely 

 any admixture of marl. These, without question, constitute the summit 

 of the Triassic system in this region. They are, however, not always 

 white ; or at least in some places, as, for example, in the vicinity of Tuba, 

 they are underlain by a still thicker bed of soft brown sandstone, which 

 is somewhat argillaceous and easily worn by the wind, forming chimney 

 buttes and ruins. This bed has a thickness along the headwaters of 

 the Moencopie Wash of about 200 feet, and is overlain at the highest 

 points by the white sandstones to a thickness of 100 feet more. These 

 sandstones are very porous and all the waters that fall in that region 

 immediately pass through them; but as they approach the summit of 

 the much harder and firmer beds that constitute the lower formations 

 these waters are arrested and come out in the form of springs, sometimes 

 almost of small rivers, along the crest of the cliffs above the Moencopie 

 Wash. It is on one of these springs that the little Mormon town of 

 Tuba is located, and this is true also of Moa Ave, Willow Springs, and 

 other settlements in that country. Still farther back the Cretaceous 

 lignites and limestones lie unconformably upon these uppermost sand- 

 stones of the Trias, and the Jurassic is wanting altogether. 



PALEONTOLOGICAL RELATIONS. 



Having thus briefly' sketched the stratigraphical relations of the 

 Older Mesozoic rocks of Arizona, I shall next consider their paleonto- 

 logical relations, in so far as they were ascertained on this expedition, 

 as shedding light upon the age of the group. 



