IV] PRESERVATION OF PLANTS 59 



identification. In his Testimony of the RocJcs, Hugh 

 Miller speaks of fossil wood from the upper beds of 

 the Jurassic system in sufficient abundance on the 

 beach at Helmsdale in Sutherlandshire to be collected 

 in cart-loads ; it is still easy to pick up good speci- 

 mens on the shingle beach a short distance north of 

 Helmsdale, and a recent microscopical examination 

 showed that some specimens are pieces of an Arau- 

 carian tree. 



Impressive examples of petrified trees on a 

 large scale are to be seen in the United States, 

 in Arizona and the Yellowstone Park. (Frontispiece.) 

 In the northern part of Arizona the country for over 

 an area of 10 square miles is covered with tree trunks, 

 some reaching 200 feet in length and a diameter of 

 10 feet. The nature of the mineralising substance has 

 given rise to the name Chalcedony Park for this 

 Triassic forest (34). A striking example of one of the 

 Arizona trees is exhibited in the British Museum and 

 in a neighbouring case is a splendid petrified stem, 9 ft. 

 in height, of a conifer discovered in Tertiary lavas in 

 Tasmania (35). 



Figure 6 illustrates the preservation of a series 

 of forests of Tertiary age in the mass of volcanic 

 sediments, 2000 feet in thickness, known as Amethyst 

 mountain, in the Yellowstone Park district. By the 

 Aveathering away of the surrounding volcanic material 

 the tall stems of the trees are exposed in places on 



