Tin-: OLDKH MKSO/OIC OF ARIZONA. 37 



ered iho entire Pnleozoic terrane, at least as far west as Bill Williams 

 Mountain and Supai. 



rilK FAlXTh'D DESERT FORM ATI OX . 



It was remarked that an exception would l)e noted to the general 

 statement that petrified wood, so far as known, is exelusively confined to 

 the Shinarunip. When at Tuba I made an excm'sion to the northeast, over 

 the brown rocks of that i-egion, and in some of the buttcs and chimneys 

 which tliev form I obserxcci black spots. \ casual examination would lead 

 to the supposition that they might be deposits of manganese or linionite. 

 They are mostly l)lack sand, but more extensive observations revealed 

 the fact that they are due to the former presence of tnmks of trees, and 

 in one place I found the remains of a log broken into a number of sections. 

 It consisted, however, wholly of the black sand and had lost all signs of 

 structm-e. Beds of lignite were reported in that general vicinity, and they 

 are prol:)al)ly due to the same cause. 



SECTIONS. 



■ Special attention was paid throughout the expedition to working 

 out geological sections of the beds studied. The more important of them 

 will be introduced here as necessary to complete the cles(;ription of the.se 

 beds. I will begin with the first section made, which resulted from an 

 investigation of the bluffs of the Little Colorado below Tanners Crossing. 



SEfTlUS I.— CANYON OF THE LITTLE COLORADO. 



[PI. IV, A-B.] 



There are a few short canyons in the Little Colorado at various 

 points, l)ut it is not until Tanners Crossing is reached that the canyon 

 becomes continuous to the mouth of the river. For several miles the 

 valley even hei'e is somewhat broad, the bed of the stream usually hugging 

 one bluff or the other; but the bluff's are always 100 to 400 feet high and 

 more or less perpendicular, so that it may be practically regarded as a 

 canyon. The fall of the river is hei-e about 25 feet to the mile, and its 

 course is nearly northwest. As the dip of the rocks is northeast this 

 would practically be the line of strike, but the fall in the rivei- is to be 

 taken into account, and it is also true that just at this point the trend of 

 all the different subdivisions is much more northerly, as I have shown in 

 my discussion of the variegated marl buttes. The consequence is that in 

 reality the bed of the river, from Tanners Crossing on, continues to be lower 



