414 ON THE GEOLOGICAL RELATIONS 



presenting also a radiated crystallization. But these 

 facts are not sufficiently generalized to allow of any 

 conclusions: if there are such leading effects, we must 

 probably seek the causes in the history of the rocks 

 themselves, not in the nature of the organic bodies. 



Incrustations must not be confounded with petri- 

 factions. In this case, the organic body is simply 

 involved; and these are also generally of recent date. 

 On the great scale, they are all calcareous, and are 

 without interest, except where they occur in the 

 travertines of Italy, where they have often given rise to 

 errors of moment. But there are two of a different 

 nature which demand notice, though the interest is of 

 a limited nature. 



I have proved, in the Geological Transactions, what 

 had been denied, that minute vegetables were pre- 

 served in chalcedony, as I have there equally proved 

 it of insects. These are the so-called moss agates: 

 but care must be taken not to confound chlorite with 

 these remains, it being the cause of the appearances 

 resembling confervae; crystallizing thus, by the con- 

 tinued superposition of its scales. In my collection, 

 three or four mosses, one possibly a Jungermannia, and 

 a Lichen, admit of no dispute; as it is equally easy to 

 account for the fact, by the familiar infiltration of 

 chalcedony into open cavities. In the same manner, 

 insects may be entangled; and thus have two ex- 

 amples occurred, my own a lepidopterous Pupa. It 

 is also said that an insect has been found in menilithe. 

 Insects are sometimes also incrusted with amber, as is 

 familiar. The remains in chalcedony may 'be of any 

 modern time: but those in amber must be as old as 

 the lignites of the older alluvia with which they occur. 

 The explanation of this is, also, easy: the substance 

 is the resin of former trees, bituminized, as the wood 



