106 Dr Davy on detached Rocks in Barbadoes, 



other inflamed parts ; and thus presenting, as it were, a link 

 in this resemblance between inorganic and organic nature. 

 Chemically examined, it was found to consist chiefly of car- 

 bonate of lime, with a little carbonate of magnesia, and a 

 trace of silica and vegetable matter. 



The likeness of this substance to agaric mineral has led 

 me to conjecture that the agaric mineral itself may owe its 

 origin to the same causes or circumstances as this substance, 

 which I believe to be the deposition of carbonate of lime on 

 a low form of vegetation, such as mucor, itself prone to de- 

 composition, and probably yielding a portion of carbonate of 

 lime, and it may be the whole of the carbonate of magnesia, 

 and the silica in the process of decomposition. A portion of 

 the green mucor that I detached, and brought away, I found, 

 on exposure to the sun, to become white, which may account 

 for the perfect whiteness of the incrustation, though contain- 

 ing a minute portion of vegetable matter. The presence of 

 this vegetable matter may be a modifying circumstance in 

 relation to the light and crumbly state of the deposition, and 

 its peculiar structure. I found that when it was acted on by 

 a dilute acid, the solution formed contained a little of this 

 matter, indicated by a greenish hue being imparted on the 

 addition of ammonia ; and, farther, that when the lime was 

 thrown down in the form of carbonate by the addition of 

 sesqui-carbonate of ammonia, it did not adhere to the side of 

 the glass vessel, or to a glass rod, as it usually does, and on 

 examination by the microscope it was found to be in globular 

 particles varying in diameter from ^^ oVo ^^ toVo of ^^ inch. 



In a former paper* I have noticed the fact, that the pre- 

 sence of some vegetable matter in solution has prevented the 

 separation, in the form of crystals, of a very crystallizable 

 salt, — the double phosphate of magnesia and ammonia, and 

 have referred to it in explanation of the amorphous state 

 in which urinary calculi often occur. The same fact may 

 apply to carbonate of lime in other instances than the one 

 above mentioned ; and if we suppose that the substance of 



• Miscellaneous Chemical Observations, in Philosophical Journal, vol. xli., 

 p. 263. 



