18 



of living trees do. Four very large roots may be seen 

 issuing from the trunks, and extending, some of them, about 

 a foot before they are lost in the surrounding stone. There 

 is nothing to indicate the species of tree of which the mould 

 has been here preserved. From the appearance of the roots 

 it is obvious that it was not a fir ; it had more resemblance 

 to a beech : the bark has been so completely bituminized, 

 that its usual characters are effaced. The petrifaction, 

 however, is not without its value ; it demonstrates that the 

 sandstone has been formed at a period posterior to the 

 existence of large trees, and that the water-worn appearance 

 of the quartz pebbles of which the sandstone is composed is 

 not a deceitful indication." Hence the ingenious observer 

 is led to remark, that " if the sandstone, which constitutes 

 so great a proportion of the coal beds, be a formation pos- 

 terior to the earth being covered with wood, we can entertain 

 no doubt that this is the case also with the slate clay and 

 the coal which alternate with this sandstone. Indeed, if 

 the coal formation exists as a portion of the old red sand- 

 stone, we can entertain no reasonable doubt that the old red 

 sandstone itself has been formed after the earth was covered 

 with wood." — Annals of Philosophy ^ Nov. 1820. 



The size which these fossil plants have attained, com- 

 pared with that of the cactuses known in Europe, must, as 

 in the fossil last mentioned, lead to a doubt as to this opinion 

 of their agreement with the recent cactus. But to be 

 enabled to form a correct judgment on this point, it is 

 necessary to know the state in which these plants exist 

 where the soil and climate are such as to allow them to 

 develope themselves in their native luxuriance. The re- 

 searches of the celebrated Humboldt, in the equinoctial 

 regions, supply us on this head with the most appropriate 

 and satisfactory information. The following detached ob- 

 servations of that philosopher will show not only the size to 

 which these plants may arrive, but the vast tracts which, 



