296 PETRIFIED FORESTS OF ARIZONA. 



wood. Even on the east it would he difficult to settle this question on 

 account of the paucity of the trunks in that direction, but it could 

 doubtless be done by prolonged and careful search. On the west side, 

 however, and directly west of the southernmost area, the plateau is 

 only about 2 miles wide and has a western escarpment with another 

 valley extending both south and west of it. This plateau or elongated 

 mesa is highest on its western side, rising to the 6,750-foot contour 

 line immediately above the escarpment, and here is exposed a tine 

 series of petrified trunks fringing the mesa, with many weathered out 

 on the slope or rolled down into the valley below. A few feet below 

 the actual summit is a bed some 20 feet thick of coarse, gray, con- 

 glomeratic, cross-bedded sandstone, at many places in which were 

 found firmly embedded logs and branches of the petrified wood, often 

 projecting from it in the cliffs and clearly in place. This, then, is the 

 true source of the fossil wood, and after several days study on all 

 sides of the area I became convinced that no other layer holds any of 

 it, at least in this region. 



This bed was found at nearly all points where the requisite elevation 

 can be attained, but the petrified logs do not occur in the same abun- 

 dance throughout. They are massed or collected together in groups or 

 heaps at certain points, and may be altogether absent at others. From 

 their great abundance in the three areas above described, which may 

 be called the upper, lower, and middle forests, respectively, but in all 

 of which they are out of place and lie several hundred feet below their 

 proper position, it must be inferred that the stratum which holds them 

 was especially rich, and the trunks must have lain in heaps upon one 

 another. This bed may have been considerably thicker in these areas 

 than it is farther out on the margins, where it is now found in place. 



Only at two points within the general petrified forest area did I find 

 remnants of this bed which had not been broken down and disinte- 

 grated. One of these is at the extreme northern end, half a mile 

 northeast of the upper forest. Here there is a small mesa, which lies 

 at an elevation of nearly 5,700 feet, or about 400 feet above the valley 

 which contains the upper forest. It is isolated and its nearly flat top, 

 which is approximately circular, is about half a mile in diameter. The 

 coarse conglomeratic sandstone stratum, 20 to 30 feet in thickness, 

 occupies the summit of this mesa and is often hardened into rock, but 

 in all essential respects it is identical with that of the elongated mesa 

 on the southwest side of the area above described. The petrified wood 

 is less abundant here, but sufficiently common, and is embedded in and 

 often projects from the sandstone ledges. 



77i£ JVatural Bridge.— Besides the fact that this bed lies wholly 

 within the petrified forest area, there is another important circum- 

 stance which serves to give it special prominence. One of the most 

 celebrated objects in this entire region is the well-known "Natural 



