445 



appearance, sufficiently testifies it to have been originally the root of 

 a tree; bat of what tree, certainly, no judgment can be formed. 

 From the manner in which these bodies are spoken of, by the older 

 writers on these subjects, it appears to be evident, that they have 

 frequently referred to this head merely some of those tufaceous in- 

 crustations, which form round pieces of twigs and branches of wood; 

 and which, from their sometimes also resembling the fragment of a 

 bone, were generally known by the name of Osteocollce. Gesner, in 

 his excellent Dissertation on Petrifactions, is obviously of this opi- 

 nion : he says, speaking of Rhizolithi, " Hue pertinent petrificata 

 ramosa calcaria, arenacea, argillacea corruptarum in terra radicum 

 sedem occupantia, Osteocollae et Stelechita3 dicta*/' Indeed, so 

 much confusion has existed with respect to this substance, that 

 many have confounded it with the stalactite, although the truly 

 respectable Aldrovandus had, at that early period, fully marked 

 the difference. The term Rhizolithus has also been applied, by some, 

 to substances which have obtained their form, from the remaining 

 earthy particles of roots, and which, being blended with other earth, 

 in the mould of the decayed root, have preserved somewhat of their 

 original form ; but, the vegetable structure being entirely destroyed, 

 they can only deserve to be considered as the vegetabilia terrificata 

 of Wallerius. 



I have hitherto supposed that bituminization was a process, to 

 which all vegetable matter was subjected, under certain circum- 

 stances; and that by this operation it became liable to the influence 

 of another process, that of petrification. But the absence in ge- 

 neral, of roots, from the collections of petrifactions, points out such 

 a deviation from this assumed law of nature as seems particularly 

 to demand investigation ; by which we may; perhaps, be enabled to 

 determine, whether this supposed la\v has been admitted upon false 



* Joannis Gesneri Tractatus Physicus dc Petrificatis, p. 21. 



