294 PETRIFIED FOKESTS OF ARIZONA. 



cedoiiy, opals, and agates found among them, ))ut many approach the 

 condition of jaspar and onyx. The degree of hardness attained by 

 them is such that they are said to make an excellent quality of emery. 

 Perhaps the most prominent of all the scenic features of the region 

 is the well-known Natural Bridge, consisting of a great petrified trunk 

 lying across a canyon and forming a footbridge over which anyone 

 mav easily pass. For reasons that will be obvious, the full treatment 

 of this feature is deferred to a more appropriate place. 



LOCATION OF THE PETRIFIED FORESTS. 



It should be understood that petrified or silicified wood occurs in 

 great quantities throughout the Triassic terrane of Arizona, New Mex- 

 ico, and Utah, and there are hundreds of places where the logs are 

 massed together or even piled one upon another; but the particular 

 region known as the "Petrified Forest of Arizona" lies in the area 

 between the Little Colorado and the Rio Puerco, 15 mi'.es east of their 

 junction, 17 miles east of Hoi brook, and 6 miles south of Adamana 

 station on the Santa Fe Pacific Railroad, which measurements termi- 

 nate at the outer edge of the area on the west and north sides. It is 

 about 8 miles square, and falls chiefl}^ within township 17 north, range 

 24 east, but extends a short distance on the south into townshio 16 

 north, and on the west into range 23 east. 



This region consists of the ruins of a former plain having an altitude 

 above sea level of 5,700 to 5,750 feet. This plain has undergone exten- 

 sive erosion to a maximum depth of neari}^ 700 feet, and is cut into 

 innumerable ridges, buttes, and small mesas, with valleys, gorges, and 

 gulches between. The strata consist of alternating beds of clays, 

 sandstone shales, and massive sandstones. The clays are purple, white 

 and blue, the purple predominating, the white and blue forming bands 

 of different thickness between the others, giving to the cliffs a lively 

 and pleasing effect. The sandstones are chiefly of a reddish brown 

 color and closely resemble the brownstone of the Portland and Newark 

 quarries, or the red sandstone of the Seneca quarries on the Potomac 

 River and at Manassas in Virginia, but some are light brown, gray, or 

 whitish in color. The mesas are formed by the resistance of the mas- 

 sive sandstone layers — of which there are several at different horizons — 

 to erosive agencies, and vary in size from mere capstones of small 

 buttes to tables several miles in extent, stretching to the east and to 

 the northwest. 



The drainage of the area is to the south, and in the middle of it, 

 having a nearly due southern course, but winding much among the 

 buttes, is the arroyo which has been mistaken for the famous Litho- 

 dendron Creek, so named by Lieutenant Whipple in 1853.' It is dry 

 most of the year, but has a gravelly bed, often 20 feet in width, and 



1 See Twentieth Annual Report U. S. Geologieal Survey, Part II, p. 324. 



