THE OLDER MESOZOIC OF ARIZONA. 23 



posed to form several quite distinct subdivisions. Indeed, I was of 

 this opinion during most of my stay in the lower Little Colorado Valley, 

 but even before leaving there the proofs of their homogeneity had 

 become apparent. 



At least the lower half consists of those remarkable beds in which 

 I had originally found the vertebrate bones in 1899, and in which alone 

 thus far vertebrate remains have been observed. I have sometimes desig- 

 nated them the variegated marls and sometimes the Belodon beds. 

 The distinguishing feature of these beds is the presence of great num- 

 bers of small buttes, the smaller ones appearing to be blue clay knolls, 

 but the larger ones showing other colors, especially purple, and some- 

 times several bands of different hues. Almost everywhere at this horizon 

 there exist plains, dotted all over with these remarkable little buttes, 

 varying from 3 or 4 feet to 20 or 30 feet in height, usually isolated from 

 one another and having a form pecuhar to them. They are not conical 

 in the true sense of the word, since they do not rise to a point at the 

 summit, but are always rounded off and have the form of a well-made 

 haystack, the smaller ones looking like haycocks in a field. These 

 butte-studded plains are of course simply the remains of a plateau or 

 mesa which has been worn away, primarily by the action of water, 

 but for a very long period there can be no doubt that wind has been 

 the more potent agency. There is evidence throughout that entire 

 region that the amount of precipitation was formerly much greater 

 than at present, and in so speaking I do not refer to a very remote date 

 geologically, but to a period which was probably post-Tertiary. Indeed, 

 from the present condition of many of the regions in which we know 

 that the early Indians dwelt and which are now perfectly dry, with 

 all sources of water so remote that they can no longer be inhabited, 

 it must be inferred that there has been a change in the climate within 

 the period of human occupancy. Certain it is that water is doing very 

 little relatively in this region now, while the agency of wind is conspic- 

 uously marked wherever it can produce effects. The pecuhar form 

 of these buttes is not such as water could have produced, while it is 

 precisely the form that wind would naturally produce, acting upon 

 the very fine and soft materials, somewhat resembling ashes, that com- 

 pose these buttes. 



