On Crystallography* 14 ^ 



lated in the liquid, without having occasion to be sup- 

 ported. 



This is not the case with the bodies which we are now 

 about to consider. The modifications which they present 

 are owing to certain local circumstances, such as points of 

 attachment, props or moulds which influence their form. 

 We unite ail these modifications under the common de- 

 nomination of concretions, which in the ordinary accepta- 

 tion signifies a congealed or fixed substance. 



But in order to fix in a more precise manner our ideas on 

 this head, we shall comprehend under the term concre- 

 tion^, the different bodies, the aspect of which depends, 

 partly at least, on their molecules being in contact with 

 other bodies. We shall now give an idea of the various 

 circumstances which contribute to vary this appearance. 



1. Stalactites, The water which filters into the fissures 

 of stones situated in the arched part of subterranean cavi- 

 ties, or which oozes through the lax and porous texture of 

 these vaults, arrives at the surface after hollowing out ccrtaiil 

 stony molecules which are united to it in any way. The 

 drops which remain suspended from the arch during a cer- 

 tain time, undergo a desiccation, which commences on the 

 external surface -, and the stony molecules which the li- 

 quid gets rid of, exerting their attraction on each other, 

 and attracted at -the same time by the side of the vault 

 which they adjoin, form in this place an initial tube, or 

 kind of small ring. This rudiment of tube increases and 

 grows longer by the intermedium of other drops, which 

 succeed to the first, conducting new molecules which th^ 

 orifice of the tube attracts in its turn. Sometimes this tube 

 preserves the form of a hollow cylinder, similar to a quill. 

 But frequently it increases in size, and is enveloped with 

 concentric layers, the matter of which is furnished by the 

 liquid which descends along the external surface. . It then 

 becomes a thick cylinder or cone ; and sometimes the mo- 

 lecules iTollowed out by the drops which thus flow into the 

 interior of its canal, finish by obstructing it entirely. These 

 different modifications are peculiarly sensible in bodies 

 which belong to carbonated lime. 



But a part of ^he liquid, on falling from the arch upon 

 the ground, forms there other depositations composed of 

 strata generally undulated, or protuberances, the figures of 

 which vary ad infinitum. Lastly, the liquid which flows 

 along the lateral partitions gives rise to bodies, tiie form of 

 which w^e might compare to that of a drop of congealed 

 water, 



K 3 Stalactites 



