rOSSIL FOEESTS OF YELLOWSTONE PARK. 



9 



Mr. Arnold Hague gives the following graphic account of this and 

 adjacent areas: 



From one end to the other the Absarokas present a high, imposing plateau, 

 with elevations ranging from 10,000 to over 12,000 feet above sea level. The 

 entire mass is made up almost exclusively of Tertiary igneous rocks. * * * 

 Degradation of the mass has taken place on a grand scale. Vast quantities of 

 volcanic ejectmenta have been removed from the summit, but no reliable data 

 exist by which the amount can be estimated even approximately. All the higher 

 portions have been sculptured by glacial ice. Enormous amphitheaters have 

 been carved out of the loose agglomerates, and peaks, pinnacles, and relics of 

 great table-lands testify in some measure to the forces of erosion. The plateau 

 is scored by a complete network of deep valleys and gorges, which dissect it in 

 every direction, and lay bare the structure of the vast volcanic pile.^ 



Within the park there is evidence of similar volcanic activity, and 

 it is clear that the basin between the encircling ranges Avas filled to 

 iis present elevation by volcanic flows, wdiich formed the present 

 park plateau. The area within which the fossil forests are now 

 found was apparently in the beginning an irregular but relatively 

 flat basin, on the floor of which after a. time there grew the first 

 forest. Then there came from some of the volcanoes, probably tliose 

 to the north, an outpouring of ashes, mud flows, and other material 

 which entirely buried the forest, but so gradually that the trees were 

 simply submerged by the incoming material, few of them being pros- 

 trated. On the raised floor of the basin, after a time, the next forest 

 came into existence, only to be in turn engulfed as the first had been, 

 and so on through the period represented by the 2,000 feet or more of 

 similar beds. The series of entombed forests atfords a means of 

 making at least a rough estimate of the time required for the up- 

 building of what is now Specimen Ridge and its extensions. (See 

 P-29.), 



During the time this 2,000 feet of material was being accumulated, 

 and since then to the present day, there has been relatively little 

 warping of the earth's crust at this point ; that is, the beds were then, 

 and still are, practically horizontal, so that the fossil forests, as they 

 are being gradually uncovered, still stand upright. 



When the volcanic activities had finally ceased, the ever-working 

 disintegrating forces of nature began to tear and Avear down this 

 accimiulated material, eroding the beds on a grand scale. Deep can- 

 yons and gulches have been trenched, and vast quantities of the softer 

 materials have been carried aAva}^ by the streams and again deposited 

 on lower levels or transported to great and unknoAvn distances. 



As the material in Avhich the fossil forests are noAV entombed con- 

 sist of ashes, mud floAvs, breccia, and the like not all the beds are of the 

 same texture and hardness, so that erosion has acted luieA^enly on 



1 Hague, Arnold, Early Tertiary A'olcanoes of the Absaroka Range: Geol. Soc. Wash,, 

 Presidential Address, 1899, p. 4. 

 36090°— 21 2 



