96 TERMINOLOGY. 



for the elevations and depressions of the mould are likewise expres- 

 sed in the cast, which in this case is the pseudomorphosis. The 

 surface sometimes bears a new coating of very minute crystals, of 

 the species of which the pseudomorphoses consists. This is frequent 

 among the pseudomorphoses of Quartz, which affect the form of Car- 

 bonate of lime. It is merely accidental however, and therefore not 

 to be classed among the peculiar and constant characters of such 

 productions. 



Pseudomorphoses are frequently hollow; and their cavities are 

 lined with crystals, or with reniform and other imitative shapes of 

 that species, which constitutes the pseudomorphoses. 



Pseudomorphoses are compound minerals, even though on ac- 

 count of the minuteness of the individuals, the composition should 

 no longer be perceptible. They are also very often mixed, since 

 several species may obviously be deposited in an impression at the 

 same time, in the same way in which several species may enter 

 into the composition of a geode. 



Pseudomorphoses cohere immediately with the adjacent mass, and 

 therefore seem only to be implanted. 



Mere coatings of crystals must not be included under pseudo- 

 morphoses, since the latter are produced by the process of subse- 

 quent formation in a mould, as it has been explained above. Nor 

 can it be allowed, to consider decomposed or otherwise destroyed 

 varieties of one species, as pseudomorphoses of another. Thus, 

 the decomposed crystals of red Oxide of Copper, can never become 

 pseudomorphoses of Carbonate of Copper, &c. 



The origin of another remarkable appearance, is so nearly related 

 to that of pseudomorphoses, that there is no place more suitable than 

 the present, for its illustration. 



Sometimes it happens, that the regular structure of a simple min- 

 eral is impressed into the mass of another, which enters into fissures 

 parallel, or dependent upon this structure. If now, the simple min- 

 eral, by some accident, is decomposed, the remaining compound one 

 will represent a shape which entirely depends on the structure of 

 the decomposed individuals. The same takes place if the individu- 

 als of compound minerals do not cohere from all sides, so that they 

 allow of the interposition of foreign matter. Thus, the cellular 

 shapes arise, of which the former have been called regular, and 

 the latter irregular, cellular shapes. The sides of the alveolae are 

 also sometimes lined with minute crystals of a third mineral. Thus 

 we find cellular shapes in Quartz, produced by Galena, and whose 

 sides are lined with Iron Pyrites. 



