The Encyclopedia Americana (1920)/Forests, Petrified

FORESTS, Petrified. Logs of trees petrified or replaced by silica and buried in sands and clays occur in various geological formations

in many parts of the world. Probably the most notable occurrence of this kind is the petrified forest in northeastern Arizona. This forest or series of forests lies 9 to 16 miles south of Adamana, a small station on the Santa Fé Railroad. They are so remarkable that in 1906 they were made a National Monument by President Roosevelt and placed in charge of a keeper under control of the Department of Agriculture. The trunks are all prostrate and mostly broken. They were of Araucarioxylon arizonicum, now extinct but related to the Norfolk Island pine, and existed in Triassic time. They grew near by and after falling drifted down a water course, lodged in some eddy, and were finally deeply buried by sand and clay. The conversion to stone was effected by gradual replacement of woody matter by silica deposited by underground water. A small amount of iron has given the beautiful brown, yellow and red tints for which this &ldquo;wood&rdquo; is noted. In thin slices under microscope the original cell structure of the wood is beautifully distinct. Some of the trunks are six feet in diameter and more than 100 feet in length, one forming a small natural bridge, the clay having been washed out beneath it. Some logs are in place where buried, but most of them roll down slopes as the sand and clay is washed away. Petrified wood occurs at other places in Arizona and New Mexico, and there are many trunks, some upright, in the eastern part of the Yellowstone Park. See.