4 



FOSSIL FORESTS OF YELLOWSTONE PAEK. 



the trees were entombed in the upright position in which they grew, 

 by the outpouring of various volcanic materials, and as the softer 

 rock surrounding them is gradually worn away they are left standing 

 erect on the steep hillsides, just as they stood when they were living; 

 in fact, it is difficult at a little distance to distinguish some of these 



fossil trunks from the lichen-covered stumps of kindred living 

 species. Such an aggregation of fossil trunks is therefore well 

 entitled to be called a true fossil forest. It should not be supposed, 

 however, that these trees still retain their limbs and smaller branches, 

 for the mass of volcanic material falling on them stripped them down 

 to bare, upright trunks. 



