FOSSIL FORESTS OF THE YELLOWSTONE.
A region of great popular and scientific interest in the Yellowstone
Park, although as yet hardly known to the tourist, owing to the
incomplete condition of the road system, is that of the Fossil Forests
in the north-east corner of the Park. The facts which have been
brought to light concerning the origin of these forests are worthy of
particular consideration.
The trees are found to occur in different planes or horizons of
growth, one above another, until the whole series represents a
thickness of many hundreds, and possibly thousands, of feet. Going
back to the first of these growths, it is found to have been destroyed
by an outpouring of volcanic material, which partially or wholly
submerged it. After the flow had ceased, the ordinary atmospheric and
aqueous agencies began work, eroding the surface in some places and
depositing the products of erosion in others, while vegetation rapidly
covered the newly-formed soil. A subsequent flow destroyed this second
growth and gave a new horizon, on which the same process was repeated.
This continued until there were at least nine, and probably twelve, of
these consecutive growths.
[Illustration:
_Terry Engr. Co._ _U. S. Geological Survey of the Territories._
Section of Amethyst Mountains.]
The lava flows in this particular section do not seem to have been
characterized by great heat. They were composed of volcanic
agglomerate, in which there was a large admixture of mud and water,
with sufficient heat to destroy life, but not to char or consume its
products. The percolation of siliceous waters gradually turned the
arboreal vegetation into stone by the process of substitution, and
thus preserved in these silent monuments a record of the events which
once transpired there. When the last of the eruptions had ceased,
there existed in this locality a vast depth of volcanic _ejectamenta_,
composed of many layers, on each of which was standing, buried in the
layer next above, the trunks of extinct forest growths.
[Illustration:
_Terry Engr. Co._ _Haynes, Photo., St. Paul._
Petrified Trees near Yancey's.]
After the cessation of volcanic activity, the eroding agencies of the
Quaternary Period carved out the valley of the Lamar River through
these accumulated flows, and laid bare the remains of their vegetable
growths. To-day the tourist may see upon the slopes of Specimen Ridge,
side by side, the living and the dead, the little conifers of present
growth and the gigantic trunks of unknown species which flourished
there eons ago.
Some of the petrifactions are very perfect. Roots, bark, parts showing
incipient decay, worm holes, leaves--all are preserved with absolute
fidelity. The rings of annual growth may be counted, and these
indicate for the larger trees an age of not less than five hundred
years. Some of the stumps are fully ten feet in diameter. Here and
there the ponderous roots stand imbedded in the rock face of the
cliff, where erosion has not yet undermined them. In one case, a large
tree that had fallen before petrifaction lies partly exposed, both
ends being still imbedded in the rock. Some hollow trees show
interiors beautifully lined with holocrystalline quartz.
How long it took each growth to reach maturity; how long it flourished
afterward before destruction; and how long the several lava flows
suspended vegetable growth; are matters largely conjectural. But at
the very lowest estimate the time represented by these various
accumulations can not be less than five thousand years.
That these early trees were of a different species from those which
now flourish there, need not excite surprise, for climatic and other
conditions are wholly changed. But an equal difference seems also to
have prevailed between the successive growths, the trees of which were
not only unlike each other, but nearly all were of species hitherto
unknown to science. Fortunately the rare perfection of some of the
specimens, particularly of the leaves and bark, have greatly
simplified their classification, and have given valuable clues to
their geologic age.
The products of these petrifactions in time strewed the surface of the
ground with such an abundance of specimens as to give the locality its
present name. Most of the lighter specimens, and some of the heavier,
have been carried away.
Besides the general interest of these old forests to the casual
observer, they are of great value to science, for probably in no other
part of the globe can a similar chapter of its history be found more
clearly recorded.