VOL. LXIX.] PHILOSOPHICAL TRANSACTIONS. AJQ 



stream (a part of the sea near the Downs,) drew up a very curious old swivel 

 gun, near 8 feet in length. The barrel of the gun, which was about 5 feet long, 

 was of brass ; but the handle, by which it was to be turned or traversed, which 

 was about 3 feet in length, and also the swivel and pivot on which it turned, 

 were of iron, and all round these latter, and especially about the swivel and 

 pivot, were formed exceeding hard incrustations of sand, converted into a kind 

 of stone, of an exceeding strong texture and firmness ; whereas round the 

 barrel of the gun, except where it was near adjoining to the iron, there were no 

 such incrustations at all, the greater part of it being clean, and in good condi- 

 tion, just as if it had still continued in use. 



The incrustation round the iron part of this gun was also the more deserving 

 of attention, as it inclosed within it, and held fastly adhering to it on the out- 

 side, a number of shells and corallines, just in the same manner as they are 

 often found in a fossil state. There were plainly to be distinguished, on the out- 

 side of this mass of incrustation, pectens, cockles, limpets, muscles, vermiculi 

 marini and balani ; and besides these, one buccinum and one oyster ; and they 

 were all so thoroughly and strongly fixed to it, and were also converted into such 

 a hard substance, that it required as much force to separate or break them, as 

 to break a fragment off any hard rock. 



Dr. Fothergill also, who had communicated some very original conjectures on 

 this subject to the society many years ago, mentioned some further curious facts. 

 On passing through the streets of London in his walks, before the sign-irons 

 were taken down, he perceived, that on the broad stone pavements, whenever 

 he came just under any sign-irons, his cane gave a different sound, and occa- 

 sioned a different kind of resistance to the hand, from what it did elsewhere ; 

 and attending more particularly to this circumstance, he found, that every 

 where, under the drip of those irons, the stones had acquired a greater degree 

 of solidity, and a wonderful hardness, so as to resist any ordinary tool, and 

 gave, when struck on, a metallic sound : and this fact, by repeated observations, 

 he was at length most thoroughly convinced of. Taking the hint therefore from 

 hence, he made several experiments ; and, among the rest, placed 2 pieces of 

 Portland stone in the same aspect and situation in every respect, but washed the 

 one frequently with water impregnated with rusty iron, and left the other un- 

 touched : and in a very few years he found the former had acquired a very sen- 

 sible degree of that hardness before described, and on being struck gave the 

 metallic sound ; while the other remained in its original state, and suliject to the 

 decays occasioned by the changes of the weather, which we find in many in- 

 stances make a most rapid progress. He also mentioned a very curious circum- 

 stance of his having found on the sea-coast near Scarborough, many years ago, 

 part of a horse-shoe incrusted with sea sand, which was so concreted as to have 



