Till-: OLDIOli .MKS( )/()!(• OF ARIZONA. 21 



then into (rue sandstone.s. These sandstones are of a hjilit color, eon- 

 traslinfi strongly with the dark-brown sandstones of (he Moeiicopie 

 ali'eady described. They ai'e, moi'eover, always more or less cro.ss- 

 bedded and usually exhil)il lines of i)ebbles ruiuiing through (hem in 

 various directions. These are (rue sandstones, very hard, de\'oid of 

 alumina, and scarcely affected by the winds, so that their angles are 

 usually sharp and the ledges tliey form are abrupt and jagged. Although 

 the sandstones proper generally occur lower down, there is no uniformity 

 in this arrangement, and sandstones are often found in the middle and 

 conglomerates mon^ rarely at the top. But in addition to these tlie 

 Lithodendron member eml)races other classes of beds. There is a well- 

 stratified layer of thinnish sandstone shales that is often seen imme- 

 diately under the heavy sandstone cap. Some of these shales have a 

 grayish color and are highly argillaceous. These layers tend to thicken 

 even within the meml^er itself, l)ut especially farther out, and, what 

 is more significant, they often become transformed into a bluish white 

 marl. This condition can l)e seen between the beds of conglomerate 

 in places where the Lithodendron beds are comparatively thin, as in 

 the lower valley of the Little Colorado, where they are only about 300 

 feet in thickness. This feature is not very prominent, l)ut at other 

 places, as in the Petrified Forest region, where the Lithodendron beds 

 attain their maximum thickness of 700 or 800 feet, this tendency on 

 the part of certain lieds to become transformed into marls is the most 

 marked feature of the meml^er. The marls here occupy much more 

 than half of the beds. They are very varied in color, showing jjesides 

 the white and blue tints a great variety of darker ones, such as pink, 

 purple, and buff. These heavy marl beds, of which there may be se\^- 

 eral in the same cliff, are interstratified between conglomerates, coarse 

 gravels, and cross-beddecl sandstones, all of which taken together form 

 the beautifidly banded cliffs that are seen throughout the Petrifietl 

 Forest, especially along its northern flank. It thus becomes necessary 

 to include under one designation all of these varying beds, which often 

 change the one into the other even at the same horizon within short 

 distances. 



It remains to mention certain minor features, which are not uni- 

 versal, but which nevertlieless have considerable importance. In the 



