The First Forest, which lies six miles south of Adamana, contains thousands of broken lengths. One unbroken log a hundred and eleven feet long bridges a canyon forty-five feet wide, a remarkable spectacle. In the Second Forest, which lies two miles and a half south of that, and the Third Forest, which is thirteen miles south of Adamana and eighteen miles southeast of Holbrook, most of the trunks appear to lie in their original positions. One which was measured by Doctor G.H. Knowlton of the Smithsonian Institution was more than seven feet in diameter and a hundred and twenty feet long. He estimates the average diameters at three or four feet, while lengths vary from sixty to a hundred feet. The coloring of the wood is variegated and brilliant. "The state of mineralization in which most of this wood exists," writes Professor Lester F. Ward, paleobotanist, "almost places them among the gems or precious stones. Not only are chalcedony, opals, and agates found among them, but many approach the condition of jasper and onyx." "The chemistry of the process of petrifaction or silicification," writes Doctor George P. Merrill, Curator of Geology in the National Museum, "is not quite clear. Silica is ordinarily looked upon as one of the most insoluble of substances. It is nevertheless readily soluble in alkaline solutions--_i.e._, solutions containing soda or potash. It is probable that the solutions permeating these buried logs were thus alkaline, and as the logs gradually decayed their organic matter was replaced, molecule by molecule, by silica. The brilliant red and other colors are due to the small amount of iron and manganese deposited together with the silica, and super-oxydized as the trunks are exposed to the air. The most brilliant colors are therefore to be found on the surface." The trees are of several species. All those identified by Doctor Knowlton were Araucaria, which do not now live in the northern hemisphere. Doctor E.C. Jeffrey, of Harvard, has described one genus unknown elsewhere. To get the Petrified Forest into full prospective it is well to recall that these shales and sands were laid in water, above whose surface the land raised many times, only to sink again and accumulate new strata. The plateau now has fifty-seven hundred feet of altitude. "When it is known," writes Doctor Knowlton, "that since the close of Triassic times probably more than fifty thousand feet of sediments have been deposited, it is seen that the age of the Triassic forests of Arizona can only be reckoned in millions of years--just how many it would be mere speculation to attempt to estimate. It is certain, also, that at one time the strata containing these petrified logs were themselves buried beneath thousands of feet of strata of later ages, which have in places been worn away sufficiently to expose the tree-bearing beds. Undoubtedly other forests as great or greater than those now exposed lie buried beneath the later formations."