lica 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."

A very interesting small forest, not in the reservation, lies nine miles
north of Adamana.

PAPAGO SAGUARO NATIONAL MONUMENT

The popular idea of a desert of dry drifting sand unrelieved except at
occasional oases by evidences of life was born of our early geographies,
which pictured the Sahara as the desert type. Far different indeed is
our American desert, most of which has a few inches of rainfall in the
early spring and grows a peculiar flora of remarkable individuality and
beauty. The creosote bush seen from the car-windows shelters a few
grasses which brown and die by summer, but help to color the landscape
the year around. Many low flowering plants gladden the dese