DENDRITES. 



85 



condition, and plants in prodigious abundance. Accidental cases 

 of color or structure externally resembling these may be found 

 under similar conditions more or less complicated figures in 

 which it will be often easy to find such resemblances as clouds or 

 the arabesques of a tap- 

 estry give us. Fig. 1 

 represents an example 

 of this kind, from the 

 Saxonia Subterranea of 

 Mylius (Leipsic, 1709) ; 

 it is the picture of a 

 stone the fracture of 

 which exhibits spots 

 making oux the figure 

 of a fowl with her plu- 

 mage, comb, and the 

 scutels of the tarsi. 

 A class of accidents 



Of a different Character Fia. 1.-Sto NE the fracture of which presents the appear- 



ance of a feathered fowl. (After Mylius.) 



is especially fruitful of 



surprises of the kind under consideration. These are the den- 

 drites, which are very frequent in joints of rocks of all ages, and 

 of which Fig. 2 gives a very exact idea. At Romainville and 



Fig. 2. Dendrite, composed of small crystals of ferriferous oxide of manganese the acer- 

 desis of mineralogists ; found in the Assures of a lithographic limestone. (Specimen from 

 the Museum of Natural History ; half the natural size.) 



Argenteuil, near Paris, we may see in the plaster quarries that all 

 the fissures crossing the beds of marl, whatever their color, white, 



