§ 37. ORGANIC REMAINS IN THE METAMORPHIC ROCKS. 875 



animals, we seek in vain for an elementary tissue capable of 

 resisting the powerful influence of heat, except in those 

 minute beings, the Infusoria, which secrete siliceous cases 

 or shells. The shields of these animalcules, and the tis- 

 sues of some of the zoophytes, are, indeed, the only animal 

 structures that can escape destruction, in rocks subjected 

 to the effects of a high temperature ; for it is clear, that 

 if calcareous skeletons were exposed to intense heat, all 

 traces of organization would be obliterated. It would 

 therefore be hopeless to expect any indications of animal 

 organisms, except of those that were siliceous, in rocks 

 where even the lines of stratification are melted away. 



M. Ehrenberg, to whom we are so greatly indebted for 

 opening this new field of inquiry, has discovered the 

 remains of Infusoria, not only in aqueous but also in volcanic 

 products. The ferruginous or ochreous film or scum, seen 

 on the waters of marshes and of stagnant pools, or collected 

 at the bottom of ditches, sometimes forming a red or yel- 

 lowish mass many inches thick without any consistence, 

 which divides upon the bare touch into minute atoms, and 

 when dried resembles oxide of iron, is found to be wholly 

 composed of the shields of animalcules ( Gaillonella ferru- 

 (jlned) : and the formation of bog iron-ore is supposed to 

 be in a great measure dependent on these animals. A fer- 

 ruginous mass from a peat-bog, " which appears to have 

 owed its origin to the action of volcanic heat at the bottom 

 of the sea, entirely consisted of shields of Naviculce" The 

 semi-opal, and the tripoli of the tertiary deposits, are 

 wholly composed of fossil remains of this kind ; and Ehren- 

 berg distinctly states, that while in the instances above 

 mentioned, there cannot be the least doubt of the nature of 

 the organic remains, in the semi-opal of the Serpentine of 

 Champigny, and in the precious opal of the porphyry, he 

 has detected bodies so exactly similar, that although at 

 present he hesitates positively to affirm that they are 



