VOL. LXIII.] PHILOSOPHICAL TRANSACTIONS. '441 



point of a small nail projecting into the pipe; and here, it is very remarkable, 

 that, either by the dashing of the water, or rather perhaps by an effect which 

 iron has been observed to have of hastening and increasing petrification, the in- 

 crustation has gone on faster than in other parts of the same side ; but so regu- 

 larly, that, from the point of the nail to the inner cavity, there is a swelling, or 

 protuberance, so uniform, that it makes throughout nearly the same segment of 

 different circles, of which the point of the nail is the common centre; and that 

 not merely directly opposite to the nail, but throughout this whole block, and 

 even farther downwards. 



sdly. The regular increase of these segments of circles is visible in each lamina 

 of the block, and in each lamina the diameter of the circle increases in due pro- 

 portion; so that it is still nearly the same segment; though, if there be any 

 difference, it is rather a smaller portion of a larger circle; as, from the cause 

 which occasioned it one would be led to expect. And with regard to these la- 

 minas it is worth observing, that as they mark the increase of the marble uni- 

 formly all round, as the growth of a tree is marked, only the marble increased 

 inward, whereas a tree grows outward, so they seem to have become visible, and 

 to have been thus distinctly marked, by means of the water bringing, at different 

 times, more or less ochre along with the sparry matter: and this is the more pro- 

 bable, as the whole country all round abounds with beds of ochre, and the waters 

 are sometimes much tinged with it. 



4thly. The cavity left in the middle of the block is not perfectly similar to the 

 original cavity of the trunk or pipe; because the water did not flow quite uni- 

 formly over the edges, at the ends of the shoots or troughs, in consequencfe pro- 

 bably of their not lying exactly horizontally; whence more water fell upon and 

 against one part of the sides of the trunk, than against the other. 



5thly. The outside of the block has taken oft impressions of all the rough- 

 nesses, knots, and shivers of the elm boards, which composed the trunk or 

 pipe, even more accurately than they could have been taken off by wax, plaster 

 of Paris, or almost any composition whatever, and certainly much more durably. 

 There is in the Philos. Trans., vol. 6o, p. 47, (Abridg., p. 10, of this vol.)avery 

 curious paper, from R. S. Raspe, concerning the production of white marble In 

 a similar manner; in which he mentions the taking off impressions of medallions, 

 by means of petrifying waters. And a paper was read at the r. s. some time 

 ago, containing an account of several impressions, actually so taken off in a 

 short time, in durable marble, by means of a petrifying water, near Bologna in 

 Italy: when some of the impressions were also sent, both to the r. s. and to the 

 British Museum. And, as this block here described, and the whole contents of 

 the pipe, of above 40 feet in length, were formed in less than 3 years, there 

 is reason to conclude, that the water of this mine in Somersetshire is as capable 



VOL. XIII. 3 L 



