SIO Mr. Stokes's Notice respecting a piece of Recent 



was renewed, the wood had in some degree decayed and contracted ; but in the Allen Bank fossil 

 it had entirely decomposed and disappeared, leaving scarcely a trace of structure in the remaining 

 parts. These are filled up with calcareous spar, which has crystallized from a number of separate 

 points, and continued till the whole mass was united. 



I must here advert to what I have mentioned^ respecting the position of the 

 insulated petrified portions of the Allen Bank fossil, in which the structure 

 shows, that they are scarcely at all removed from the position in which they 

 grew. As these seem to have remained in their places, after the other por- 

 tions of the wood had decayed and disappeared, and before the intermediate 

 parts had been filled up by solid mineral matter, it appears to follow that they 

 must have been suspended in the fluid solution which has since crystallized 

 around them, — a condition which it is certainly difficult to comprehend. 



In regard to the piece of wood from the aqueduct, the petrified portions 

 are also separate and insulated, but as they are in long continuous columns, 

 it is probable that the whole of the wood was not equally penetrated with the 

 calcareous solution. 



The other cases I have met with, of a partial petrifaction by carbonate of 

 lime, are those of the hazel nuts at Belfast Lough, mentioned by Dr. Mac- 

 donnel, in 1810*, and of partly petrified wood and nuts, described by Mr. 

 Phillips, from the vale of the Aire, near Ferry Bridge, in Yorkshiref . In this 

 latter case, it appears that the wood and nuts are in a deposit of alluvium. 

 Many pieces of the wood, and the kernels of some of the nuts, found at a 

 depth of 12 feet, are partially petrified. 



A specimen of the wood here mentioned, which was given by Mr. Phillips 

 to Dr. Buckland, who has allowed me to examine it, is a portion of a stem or 

 branch, split longitudinally, about four inches in length, and about two and a 

 half in diameter. In this, a part near the centre, is now completely petrified 

 by carbonate of lime. This portion is about half an inch in diameter at one 

 end, and extends longitudinally through the wood to the length of about three 

 inches, and terminates in a point. It is in its natural position, and the medul- 

 lary rays are continuous through the calcareous part and the unchanged por- 

 tion, as shown in the accompanying wood-cut. 



The line of separation between the calcareous part and the unchanged wood, 

 is perfectly well defined, and although we may suppose that the vessels of 

 the wood, have acted as conductors to the solution, and given it a direction 

 longitudinally through the stem, yet it is difficult to understand why the petri- 

 faction has been confined to a single spot or column. 



* Geological Transactions, First Series, vol. iv. p. 443. 



-j- Philosophical Magazine and Annals of Philosophy, New Series, vol. iv,, 1828. 



