Art. VII. — Fossil Forests of tiac Volcanic Tertiary For- 

 mat^O£i§ of the Vellowstosae jVatiosaal Parlv. 



By \^. H. Kolmes. 



The prevalence of extraordinary volcanic activity tlironghout 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 Eocky Mountain region, 

 that, notwithstanding the frequent visits of geologists, no divisions 

 into sub-groui)s have been ipade, 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 entii'e 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 Fork of the Yellowstone Eiver, where this 

 I)eculiar group of rocks is tj7)ically developed, they have a thicliuess of 

 iil)wards of 5,000 feet. The prevailing materials which enter into their 

 composition are fragmentary volcanic i^roducts, 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 silicifled 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 GaUatin Eange 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 silicified wood occur, and near 

 the divide at the head of Boulder Creek sOicified 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 Eiver, in similar strata, there 



125 



