PETRIFIED FORESTS OF ARIZONA. 297 



Bridge," mentioned b}^ so man}- travelers and referred to in the docu- 

 ments quoted at the beginning of this report, consisting of a great 

 petrified trunk lying across a canyon and forming a natural footbridge 

 on which men may easily cross. This occurs on the northeast side of 

 the above-mentioned mesa near its rim, and the bed in which it lies is 

 the coarse sandstone which holds all the petrified wood. The Natural 

 Bridge, therefore, possesses the added interest of being in place, which 

 can be said of very few of the other petrified logs of this region. 



It was observed in the southwestern exposure and at other points 

 that all the petrified logs and blocks lying in the sandstone or only 

 recently washed out of it are surrounded by a coating of the sandstone 

 firmly cemented to the exterior. The absence of this coating from 

 most of those in the principal forests is due to their long exposure to 

 climatic influences which ultimately disintegrate and detach the sand 

 rock adhering to them and strip them clean to the body of the trunks 

 themselves. That this process requires ages of time is proved by the 

 fact that the Natural Bridge is still coated over a large part of its sur- 

 face by the remains of the cemented sand rock in which it was once 

 completeh^ imbedded. This is true chiefly of the lower portion, and 

 farther up the trunk it has nearly all disappeared. The trunk is in an 

 excellent state of preservation and is complete to the base, where it is ab- 

 ruptly enlarged and shows the manner in which the roots were attached. 

 This portion still lies partially buried in the sandstone, which is the 

 same in character as that which still adheres to the lower 20 feet. 

 The canyon or gulch has a due north direction and is very precipitous, 

 beginning only 200 yards above the bridge and rapidly broadening in 

 its descent. At the point where the bridge crosses it is about 30 feet 

 wide, but the trunk lies diagonally across and measures 44 feet between 

 the points at which it rests on the sides of the canyon. The angle is 

 nearly 45°, and the tree lies with its roots to the southeast and its top 

 to the northwest. The canyon is here about 20 feet deep, and from its 

 bottom and slopes several small trees are growing, some of which rise 

 considerably above the bridge. The trees are mostly cedars, but 

 there is one cotton wood {Populim mujiLstifolla). The root is quite near 

 the brink of the canyon, but rests on a solid ledge for a distance of 4 

 feet, so that there is no probability that in this dry region it will be 

 endangered by further erosion. The total length exposed is 111 feet, 

 so that more than 60 feet of the upper part lie out on the left bank of 

 the canyon. At about the middle of the canyon, and above where the 

 coating of sandstone still adheres, it measures 10 feet in circumference, 

 giving a diameter of over 3 feet. At the base it is now 4 feet in 

 diameter, but the thickness of the incrustation is not exactly known. 

 At the extreme summit the diameter is reduced to 18 inches. As in 

 the case of practically all the petrified logs of the region, there 



