CATARACTS, AND INUNDATIONS. 277 



<'va!itions, which yet adhere close to each other : they seldom turn 

 the wood into stone; but, sticking to the wood, plants, &c. coagu. 

 late on it, and by degrees cover it with a crust of a whitish sub- 

 stance of different thickness, by which the wood is inmierged or 

 wrapped in a stony coat, which, if it be broken before the wood be 

 rotten, you find it in the heart of the stone or incrustation, as is 

 seen it) those petrifications at Maudling meadows in Gloucestershire, 

 at Hermitage near Dublin, and many other places : or, if the wood 

 be rotten, you will find a cavity in the stone, which very often is 

 filled by a subsequent incrustation or petrification ; the stony parti. 

 cks then taking the place of the rotten wood. 



Sometimes indeed, these waters, permeating the pores of the 

 wood either longitudinally or transversely, insinuate themselves into 

 them, fill them up with their stony particles, swell, and, by their 

 burning or corroding quality proceeding from the lime-stone, de- 

 stroy the wood, and assume the shape of the plant, the place of 

 which they have taken. 



These petrifications generally ferment with acids and spirit of 

 vitriol^ and by calcination may be reduced to lime. 



Ferrugineous or metallic petrifying waters mostly act by insinu- 

 ating their finest particles through the pores and vessels of the 

 wood, or other-vegetables, without increasing their bulk, or alter- 

 ing their texture, though they greatly increase their specific gravity : 

 and such is the petrified wood found in or on the shores of Lough- 

 ueagh ; for it does not show any outward addition or coalition of 

 forcing matter adhering to, or covering it (except in some places, 

 where a thin slimy substance, taken notice of hereafter, is sometimes 

 observed.) but preserve the grain and vestigia of wood ; all the al- 

 teration is in the weight and closeness, by the mineral particles 

 pervading and filling the pores of the wood : these stones, or rather 

 wood-stones, do not make the least effervescence with spirit or oil 

 of vitriol, nor aquafortis ; which shows that they are impregnated 

 with metalline particles, or stony ones, different from the calcareous 

 kind ; and may be the reason why the petrified wood, mentioned 

 by N. Grew *, made no ebullition, at which it seems he was sur- 

 prised f. These stones he could not reduce into lime by the most 



~ ' 



* Reg. Soc. Mus. p. 270. Orig. 



+ This contradicts an ob-ervation of Mr. John Beaumont, (Phil. Trans. No. 

 129), That mostly mineral stones will stir with acids ; whereas all those that I 

 have tried, whether English or Irish, did not at all stir with acids, Orig. 



T 3 



