314 THE AMERICAN MUSEUM JOURNAL 



his own country. This necessarily limits him to the first, or possibly to the 

 first and second forests. One should devote at least two days to them, 

 passing the first day through the first and second forests and arriving at the 

 third in season to camp at the one water hole within the entire area. The 

 forenoon of the second day can well be given up to exploring the third and 

 Rainbow forests, and the afternoon to the return to Adamana. Such a 

 trip involves no hardship. Camping at the altitude of 5000 feet in the dry 

 atmosphere is simply exhilarating and the small supply of food and water 

 needed can readily be carried with the outfit which is furnished by the 

 superintendent at Adamana. 



The geology of this area was first worked out in detail by the late Pro- 

 fessor Lester F. Ward, then connected with the United States Geological 

 Survey. He described the region as consisting of the ruins of a former 

 plain having an altitude above sea level of something like 5700 feet. This 

 has now undergone erosion to a maximum depth of nearly 700 feet and is 

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

 and gulches between. The rock formations consist of nearly horizontal, 

 alternating beds of purple, white and bluish marls, sandstones and shales, 

 giving a lively and pleasing effect such as is characteristic of so many of the 

 landscapes of the state. The beds in which the logs were entombed were de- 

 posited at the bottom of a Mesozoic sea, where they remained until Tertiary 

 times when the entire country was raised from five to six thousand feet 

 above sea level. The logs throughout the area belong to a cone-bearing 

 tree, of a single species, described by Dr. F. H. Knowlton of the United 

 States Geological Survey under the name of Araucarioxylon arizonicum, a 

 tree no longer found in the northern hemisphere, its nearest representative 

 being a small cultivated form known as the Norfolk Island pine. 



As to how the trunks became petrified or silicified we are still somewhat 

 in the dark. Silica is ordinarily one of the most insoluble substances, but 

 nevertheless readily soluble in an alkaline solution — that is, one containing 

 soda or potash. It is probable that the solutions permeating through these 

 beds were of this nature and as the logs gradually decayed their organic 

 matter was replaced, molecule by molecule, by silica. The wood is there- 

 fore not " turned to stone," but has simply been replaced by mineral matter, 

 mainly silica. The brilliant red and other colors are due to the small 

 amounts of iron and manganese deposited together with the silica, and 

 super-oxidation as the trunks are exposed to the air. The more brilliant 

 colors are therefore to be found in the small chips lying on or near the sur- 

 face. 



Prior to 1906 these forests were on government and railroad lands and 

 subject to the vandalism of curiosity seekers and those commercially in- 

 clined. At one time a considerable industry was carried on in cut and 

 polished sections of the sounder and more highly colored varieties, and 



