118 GEOLOGY. 



and it finally- reposes on schistus. The petriiac- 

 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 p re tri faction. I was told 

 of three or four petrified white oaks at Chitteningo, 

 which I had not an opportunity of observing, but 

 the}' are said to lie under a gypsum hill, and to 

 be subject to alluvions from it. 1 have seen the 

 fossil tree at Pcnicuick in Scotland, which hns 

 been the subject of so much speculation, and I 

 can now account for its origin. It was produced 

 from Silicious depositions passing over a Scotch 

 pine. Tl e strata in which the remains of tlie tree 

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

 stone, and there is sand ston^ i-iiujediately above 

 the slate clay. 



I have tried tlie fissii trees ori\-r.rcL'iiUs by the 

 application c{ muriiitic acid, and I find by the 

 efiervescence unequivocal indication of a calcare- 

 ous substance. I also saw petriiied leave*;; atd 

 tliere is a strong probability that animals may 

 also be discovered in a petrified s'lape p od ed 

 in the same wav. The human skeleton which 



