Ch. XL SOUTH AMERICA. 4/7 



It must l)e observed, that the rocks and all the 

 parts which this ri\'er washes, are covered with a 

 crust of hardness httle interior to that of the main 

 rock; and this increases its volume, and distinguishes 

 itself from the oriü-inal rock, which is somethins: 

 yellowish. The inference I would draw from hence 

 is, that the water of the river is mixed v/ith petri- 

 fying, viscid, and glutinous particles, which adhere 

 to the body they surround: and as by their extreme 

 subtility they insinuate themselves through its pores, 

 they fill the place of the fibres, which the water in- 

 sensibly rots off and separates, till at length all that 

 was leaf or wood gives way to that petrifying mat- 

 ter ; which still retains the impression of the parts 

 -of the original, with its several veins, fibres, and 

 ramifications. For at the time of its insinuation, the 

 ducts of the wood, or leaves, serve for a kind of 

 mould, by which it naturally takes the entire figure 

 of the body into which it has obtruded itself. 



-An observation I made with some branches con- 

 firms me in this opinion : for, having opened them, 

 I found some leaves and bits of wood, which snapped 

 on breaking; and the inside M^as as large as real 

 stone, the texture only remaining of its first sub- 

 stance. But in others, the parts consolidated by the 

 stony matter snapped; and the fibres, not having yet 

 undergone a total corruption, retained the appearance 

 of wood, though some were more rotten and decayed 

 than others. I had also some leaves, the surface of 

 which was only covered with a very fine lapideous 

 tegument, but within were entire leaves, except here 

 and there a little mark of decay. 



It is to be observed, that this matter much 

 more easily fastens on any corruptible substance, 

 than on the more compact and solid, as stones, 

 and the like: the reason of which is, that in one 

 it meets with pores, in which it fixes itself; but 



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having 



