118 GEOLOGY. 



and it finally reposes on schistus. The petrifac- 

 tion of the tree is owing to the calcareous deposits. 

 Saturated water continually passing over it, must 

 leave some of its matter behind — and as the tree 

 decays, its vegetable loss is supplied by mineral 

 accretion — and sometimes the lime, in solution, is 

 mixed with arenaceous particles which combine 

 in the formation of the pretrifaction. I was told 

 of three or four petrified white oaks at Chitteningo, 

 which I had not an opportunity of observing, but 

 thj^y are said to ijev.nder a g3'psum hill, and to 

 be subject to aUuvieRs from it. ' i have seen the 

 fossil tree at Penicuick in Scotland, which has 

 been the subject of so much speculation, and I 

 can now account for its origin. It w as produced 

 from Silicious depositions passing over a Scotch 

 pine. The strata in which the remains of the tree 

 are, consist of slate clay, but the tree itself is sand 

 stone, and there is sand stone immediately above 

 the slate clay. 



I have tried the fossil trees of Marcellus by the 

 application of muriatic acid, and I find by the 

 effervescence unequivocal indication of a calcare- 

 ous substance. I also saw petrified leaves, and 

 there is a strong probability that animals may 

 also be discovered in a petrified shape prod ^ ed 

 in the same way. The human skeleton which 



