American
wonders is the silicified forest, known as Chalcedony Park, situated
about eight miles south of Corrizo, a station on the Atlantic and
Pacific Railroad, in Apache County, Ariz. The country formation is
sandstone on volcanic ash, and the trees are exposed in gulches and
basins where the water has worn the sandstone away, or are buried
beneath the sandstone, their ends protruding from between the
formations. (See Illustration.) The locality was noticed in 1853 by the
Pacific Railroad Exploring Survey. The jasper and agate generally
replaced the cell-walls and fibres, and the transparent quartz filled
the cells and interstices, especially where the structure was broken
down by decay. These cell-centers and cavities produced conditions
favorable not only for the deposition of silica as quartz, but also for
the formation of the drusy crystalline cavities of quartz and amethyst
that so increase the beauty of the material. There is every evidence to
show that the trees grew beside some inland sea. After falling they
became water-logged, and during decomposition the cell structure of
the wood was entirely replaced by silica from sandstone in the walls
surrounding this great inland sea. Major John W. Powell, who has
visited all these regions, says : " The wood consisted of logs
water-rolled before burial, and are now gradually weathering out of
their matrix. The enclosing rock is sandstone and cretaceous shale of
the series known as Jura-trias and lying immediately above the
Chinarump. Agatized wood containing much semi-opal has been formed in
California (and possibly in Arizona) under volcanic deposits, but the
wood in question is not associated with volcanic material; its matrix
is sedimentary."
The
red and yellow coloring matter is derived from the oxide of iron in the
sandstone, which is red, and the black may be due to partial
carbonization or to oxide of manganese. The bark in nearly every case
has been decayed before silicification, and even part of the other
layers of the tree is often gone; but the difference between the
oxidation on the surface and inside is that the surface, to the depth
of half an inch, is so altered and changed that it has the appearance
of bark, and it is generally supposed to be such.
There is every indication that the deposit is of considerable
