130 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Voir. 



basaltic fragments, many of wMcli are of great size ; tliere is, however, 

 always enough tufaceous and other fine-grained material to fill in the 

 interstices and act as a cement. These beds are massive and irregular, 

 and seem to have accumulated too fast to be thoroughly redistributed 

 by the waters. Only the stronger trees of the forest seem to have with- 

 stood the fierce storms of rocks that must have prevailed at the period of 

 then entombment, as the smaller trunks and branches are prostrate or 

 totally destroyed. In most cases where upright trunks penetrate tlie 

 entire thickness of an enclosing bed, the tops may be seen to terminate 

 with the upi^er surface of that bed, as if causes had acted at the begin- 

 ning of the deposition of the succeeding stratum to plane down the 

 irregularities of the old surface. In due course of time, this succeeding 

 stratum iDroduced its growth of forest, which followed its many prede- 

 cessors into the subterranean depths, and in its turn was buried by the 

 rapidly accumulating conglomerates. This remarkable alternation of 

 events seems, in a general way, to have been kept uj) from the beginning 

 to the end of the period. 



The very precipitous character of the cliffs prevented me from reach- 

 ing the upper part of the wall at this point, but I succeeded in making 

 my way to the summit of the mountain at two other points, and found 

 that everywhere the section was practically the same. 



On the ojjposite side of the valley the same conditions were observed: 

 the fossil trees occur at the highest point reached, 3,000 feet above the 

 river. The ranges that form the rim of this valley on the north and east 

 reach an elevation of 11,500 feet, and as the conglomerates may be seen 

 reaching and forming the loftiest summits wdthout perceptible break or 

 change of character, it is probable that they will be found to enclose the 

 remains of forests throughout. 



On some of the higher summits to the east of Yellowstone Lake, simi- 

 lar stratified conglomerates contain silicified wood in a very fragmentary 

 state. These conglomerates are composed mainly of basaltic and tra- 

 chytic materials, but contain large quantities of fragments of sand- 

 stones and quartzites, which leads to the conclusion that portions of the 

 earlier Tertiary strata have been broken up and ejected with the igneous 

 products. It is quite probable that these strata were among the later 

 products of the Volcanic Tertiary age proper. They are generally found 

 abutting against masses of unstratified igneous materials that probably 

 mark the sites of islands which were doubtless volcanic centers. I find 

 that as we recede from these centers of eruption the strata diminish very 

 perceptibly in thickness and coarseness of materials, and have at the 

 same time a very perceptible dip toward the surrounding valleys. One 

 is at times led to suspect that portions, at least, of these beds are of sub- 

 aerial formation, as is the case with extensive strata about the cones of 

 modern volcanoes, but there are a multitude of facts that go to prove 

 that the greater part of the formations of this age were rearranged or 

 sedimented in water. 



