362 THE POPULAR SCIENCE MONTHLY. 



AGATIZED AND JASPEKIZED WOOD OF ARIZONA. 



By GEOEGE F. KUNZ. 



T TNDOUBTEDLY one of the greatest of American wonders is the 

 ^ silicified forest in Arizona, known as Chalcedony Park— a park 

 only in name, however, for the giant trees which once grew there 

 have long since fallen and silicified into agate and jasper. It is situ- 

 ated eight miles south of Corriza, a station on the Atlantic and Pa- 

 cific Railroad, in Apache County, Arizona, twenty-four miles south- 

 east of Holbrook. This marvelous deposit of probably a million tons 

 of silicified trees covers a thousand acres. The wood is generally 

 found projecting from the volcanic ash and lava, which is covered 

 with sandstone to the depth of from twenty to thirty feet, and lies ex- 

 posed in the gulches and basins where the water has worn away the 

 sandstone. 



The silicification probably took place in the following manner : 

 The trees were overthrown and covered with volcanic ashes and tufa, 

 the heated silicified waters, either gushing from springs or forced up 

 by the violent volcanic action which felled the trees, percolated 

 through the ashes, cooled on reaching the tree-level, and thus produced 

 conditions favorable to silicification. 



The moisture in the tufa may have effected a partial alteration, as 

 also any waters that may have filtrated through it from rains or 

 springs either hot or cold. Under these circumstances decomposition 

 would be assisted and much silica be set free. The waters would be- 

 come charged with this, the silica being held partly in solution similar 

 to that in liquid glass, the silicate of soda of commerce. The silicious 

 water then slowly penetrated the wood buried in the tufa and was 

 slowly deposited in the cells of the wood. In this manner the fibers 

 of the wood were replaced by the silica. The process was evidently 

 a slow one, and the trees, from all appearances, were partly decayed 

 and water-logged when the silicification took place. The jasper 

 and agate generally replaced the cell-walls and fibers, and the trans- 

 parent quartz filled the cells and interstices, especially where the 

 structure was broken down by decay. These cell-centers and cavi- 

 ties produced the conditions favorable not only for the deposition of 

 the silica as quartz, but also for the formation of the drusy, crystalline 

 cavities of quartz and amethyst that enhance the beauty of the ma- 

 terial so much. It is evident, from the rich variety of colors, that the 

 waters held oxides of iron and perhaps manganese, as well as silica, 

 the red color being caused by hematite, the yellows and browns by 

 liraonite, and the black by oxides of manganese. 



It is possible also that the ash was deposited partly in water and 

 thus heated it. There is every indication that the deposit is of con- 





