FOSSIL FOEESTS. 253 



The published evidences are less numerous of pet- 

 rified forests — and curious and wonderful indeed 

 is the process by which wood is changed to stone 

 without losing the markings which distinguished 

 it when the slow process of petrifaction, ages ago, 

 commenced. How great and powerful have some- 

 times been the convulsions which in past times 

 have overturned parts of the world, and changed all 

 the then existing conditions of the life of the plants 

 and animals overwhelmed, can be learnt from the 

 great depths under the present surface strata at 

 which forestal remains are often discovered. Trees 

 are frequently dug out from positions two or three 

 hundred feet below the surface, and the deep 

 waters of lakes often overlie whole forests, although 

 sometimes the buried relics are only just below the 

 surface soil. Occasionally^ indeed, the forestal re- 

 mains lie along the surface of the ground, or are 

 but barely covered by earth or sand — the earth 

 or sand of the new soil which has taken the place 

 of that buried. 



Whilst great convulsions of Nature have pro- 

 bably occasioned the changes which have caused 

 forests and individual trees to be buried at con- 



