262 TERMINOLOGY. . 186. 



contain cavities, either empty or filled with water and other 

 fluids. These are always in close relation to the external 

 form of the crystals themselves, which is not the case in 

 the pseudomorphoses. Another class of opening", in the in- 

 terior, occasioned by other minerals being included, must 

 be referred to the impressions. 



The pseudomorphoses are compound minerals, even 

 though, on account of the minuteness of the individuals, the 

 composition should no longer be perceptible. But they 

 are also very often mixed, since several species may be de- 

 posited in an impression at the same time, in the same 

 way in which several species may enter into the composi- 

 tion of a geode. 



The pseudomorphoses cohere immediately with the adja- 

 cent mass, and therefore seem only to be implanted. 



This also is the case in certain real crystals ; but here the 

 crystals form only those parts of the individuals constituting 

 the support, which have reached the free space, and which 

 for that reason have assumed a regular form. 



Mere coatings of crystals must not be enumerated along 

 with the pseudomorphoses, since the latter are produced by 

 the process of subsequent formation in a mould, as it has 

 been explained before. Nor can it be allowed to consider 

 decomposed or otherwise destroyed varieties of one species, 

 as pseudomorphoses of another (. 21.). Thus the decom- 

 posed varieties of hexahedral Iron-pyrites can never be- 

 come pseudomorphoses of prismatic Iron-ore, nor those of 

 paratomous Augite-spar pseudomorphoses of Green-earth, 

 the latter being a variety of prismatic Talc-mica. 



The origin of another remarkable appearance, is so very^ 

 nearly related to that of the pseudomorphoses, that there 

 is no place more adapted than this for its explanation. 



Sometimes it happens that also the regular structure of a 

 simple mineral is impressed into the mass of another, which 

 enters into fissures parallel or dependent upon this struc- 

 ture. If now the simple mineral, by whatever accident, is 

 decomposed, the remaining compound one will represent 

 a shape which entirely depends on the structure of the 



