THE OLDER MESOZOIC OF ARIZONA. 25 



appear in great force in the valle}^ of Leroux Wash. Here they cover an 

 area of nearly 100 square miles and form two great amphitheaters of 

 veritable badlands. The great variety and symmetry in the form of 

 these buttes and ridges, however, as well as the variegated and iridescent 

 colors that prevail, render them a magnificent spectacle. They can be 

 seen from the southeast for a distance of 20 miles as a white line. Viewed 

 from the top of the mesa out of which they have been carved, the denuda- 

 tion having been arrested at a particular point, they reveal more com- 

 pletely than at any other place the true character of this member. In 

 the Petrified Forest the Leroux beds are also well developed, and the 

 variegated marls are found only half a mile east of the Lower Forest. 

 The buttes here are rather large and well developed, and bones of the 

 Belodont occur in them. In the northern part of the Petrified Forest 

 region the variegated marls lie somewhat farther to the east. What is 

 called the Middle Forest lies in the midst of them, and the petrified wood, 

 as everybody has observed, differs here considerably in its constitution 

 and coloration from that of the Upper and Lower forests, which lie in the 

 horizon of the conglomerate member. 



As was remarked when treating of the conglomerates, these variegated 

 marls are actually found stratified between the sandstones by the trans- 

 formation of certain shales into marls. If these beds are carefully traced 

 a short distance in the direction of the dip they will be seen to thicken 

 verj'- rapidly and soon to take on the character of the true variegated marls. 

 As they start from underneath a bed of sandstone which caps the conglom- 

 erates, and which does not so readily pass into marl, the buttes that are 

 first formed are usually topped out by a block of this sandstone, and it is 

 necessary to proceed some distance farther in the direction of the dip to 

 reach a point where the sandstones disappear. This, however, ultimately 

 takes place and the marl beds thicken to such an extent that they have to 

 be regarded as virtually overlying the conglomerates. In fact, in the 

 bed of the Moencopie Wash, on both sides of which these beds are so well 

 developed, the conglomerates can be seen distinctly passing under the 

 marls. 



For the purposes of our expedition the variegated marls constituted 

 the most important sulDdivision of the entire group. But as we have 

 seen, their maximum thickness is about 400 feet, and there remain still 



