Art. VII. — Fossil Forests of the Volcanic Tertiary For 
■nations of the Yellowstone National Park. 
By W. H. Holmes. 
The prevalence of extraordinary volcanic activity throughout that 
part of the Tertiary age represented by the post-Cretaceous rocks of 
the Yellowstone region has given to them a most unique and interest- 
ing character. So destitute of animal remains are they, and so unlike 
the formations of the age in other parts of the Boeky Mountain region, 
that, notwithstanding the frequent visits of geologists, no divisions 
into sub-groups have been made, and no more definite appellation for 
the whole group has been found than the “ Volcanic Tertiary this 
name, although so general, is singularly appropriate,- and, in the absence 
of specific determinations, may be used to designate the entire group of 
Tertiary strata in the Park district. 
It is not my intention in this brief notice to attempt the classification 
or correlation of these strata, but to give a brief account of some very 
remarkable features brought to light by last year’s explorations. 
In the valley of the East Pork of the Yellowstone Biver, where this 
peculiar group of rocks is typically developed, they have a thickness of 
upwards of 5,000 feet. The prevailing materials which enter into their 
composition are fragmentary volcanic products, which have been appar- 
ently redistributed by water, and now form breccias, conglomerates, and 
sandstones. It has been noticed by nearly all visitors that these strata 
contain a great abundance of silieified wood, and in a few cases trunks 
of trees in situ have been reported. The lowest observed occurrence of 
the strata of this group is in the valley of the main Yellowstone, between 
the first and second canons, at an elevation of about 5,000 feet above the 
sea. They are also finely developed in the Gallatin Bange to the west of 
this valley, and about the sources of Canon and Boulder Creeks reach 
a thickness of between 3,000 and 4,000 feet. At a number of points 
covering this entire thickness, masses of silieified wood occur, and near 
the divide at the head of Boulder Creek silieified trunks, many feet in 
height, and of gigantic proportions, stand in the identical strata in 
which they grew, the crumbling conglomerates having withered away, 
leaving them standing upright along the steep slopes of the mountain. 
In general, these strata are horizontal. The bedding is often heavy, and 
in places not well marked; sub-aerial volcanic deposits apparently alter- 
nate to some extent with the sub-aqueous. 
Three miles above the mouth of Gardiner’s Biver, in similar strata, there 
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