1 50 On Crystallography, 



Stalactites are those bodies which are formed in the arch 

 of the vauh ; and stalagmites are those which originate 

 from the falhng of the hquid on the ground. It is, how- 

 ever, much mit)re convenient to call both stalactites, as it 

 is sometimes difficult to distinguish between the two kinds 

 of formation, when the bodies under consideration have 

 been removed from their original position. 



2. Iiicr7istationSj In the preceding concretions, the aggre- 

 gation of the molecules depends more especially on the 

 evaporation of the liquid which has flowed over them. 

 Other concretions, which have been called incrustations, 

 iufs, and si?itcrs, proceed from a kind of precipitaticm of 

 the molecules originally suspended in the liquid. The 

 latter are sometimes deposited on the surface of different 

 organized bodies, particularly on those which belong to 

 the vegetable kingdom, and sometimes cover .the inside of 

 certain bodies, such as sewers or drains. 



When the liquid is introduced into a subterranean cavity 

 of small dimensions, ^ where it can remain, the stony mole- 

 cules incrust the sides of this cavity, which is generally of a 

 round form, and sometimes end by studding it with crystals. 

 This IS what has been called geode. Some of these bodies 

 contain a solid and moveable nucleus, or a pulverulent 

 earthy matter* ; of this description also are certain pieces 

 of silex found in marie. Sometimes also the geode is en- 

 tirely filled with a matter which may be distinguished by 

 the naked eye from that of which it is itself composed. 



It may also happen that a substance may be incrusted 

 with crystals of a different nature, by being as if moulded 

 along with them. For instance, we are acquainted with 

 crystals of metastatic carbonated lime incrusted with 

 quartz, and sometimes the quartzous envelope remains 

 empty after being separated from the crystals which it 

 concealed. 



3. Pseiidomophoses, There exists a third order of 

 concretions which we call pseudomorphoses, i. e., bodies 

 ■which have a false and deceitful figure ; because the sub- 

 stances which belong to this order present in a very remark- 

 able manner foreign or strange forms, which they have in 

 some measure obtained from other bodies which had re- 

 ceived them from natur^. ' ■ 



When the type of this apparent transformation is a 

 shell, it happens frequently enough that the shell still covers 

 in whole or in part the substance, which is as if moulded 



♦ It is probably from this that the term geode is derived, i. e., a body 

 Vhich contains earth, 



into 



