758 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. 



been accumulated and not fewer than fifteen forests were entombed. Then 

 the volcanoes ceased their activity and final quiet was restored. Probably 

 an upward tendency was given to the area, but it must have been very 

 gradual and not attended by the distortion which so frequently accompanies 

 mountain building. The disintegrating action of frost and rain immediately 

 set in and has carved out this mountain, in the heart of which may be 

 read the story of its origin. 



In the foothills and several hundred feet above the valley there is a per- 

 pendicular wall of breccia, which in some places attains a height of nearly 

 100 feet. The fossil trunks may be seen in this wall in many places, all of 

 them standing upright in the positions in which they grew. Their upright 

 position proves that if there have been changes of level they have been 

 gradual and in the same plane, as otherwise the trunks would be variously 

 inclined. Some of these trunks, which are from 2 to 4 feet in diameter 

 and 20 to 40 feet in height, are so far weathered out of the rock as to 

 appear just ready to fall, while others are only slightly exposed. Niches 

 mark the places from which others have already fallen, and the foot of the 

 cliff is piled high with fragments of various sizes. 



Above this cliff the fossil trunks appear in great numbers and in regular 

 succession. As they are perfectly silicified they are more resistant than the 

 surrounding matrix, and consequently stand out above it, In most cases 

 they are only a few inches above the surface, but occasionally one rises as 

 high as 5 or 6 feet. 



The largest trunk observed in the Park is found in this locality. It is 

 a little over 10 feet in diameter, which includes a portion of the bark. It 

 is very much broken down, especially in the interior, a condition which 

 very probably prevailed before fossilization. It projects about 6 feet above 

 the surface. 



The most remarkable of all the forests, however, is located on the west- 

 ern end of Specimen Ridge, about 1 mile southeast of Junction Butte and 

 opposite the mouth of Slough Creek. It was first brought to the notice, of 

 the scientific world by Mr. E. C. Alderson and the writer, who discovered 

 it in August, 1887. It is found on the higher portion of the ridge, and is 

 several acres in extent. The trees are exposed at various heights on a 

 very steep hillside, and the remarkable feature is that most of them project 

 weil above the surface. 



