THEORY OF THE EARTH. 



been deposited from fresh water, or certain allu- 

 vial beds of very ancient formation, generally 

 composed of sand and rounded pebbles ; which 

 were perhaps the earliest alluvial formations of thje 

 ancient world. Along with these there are also 

 found some lost species of known genera, but in 

 small numbers ; together with some oviparous 

 quadrupeds and some fish, which appear to have 

 been inhabitants of fresh water. The strata con- 

 taining these are always more or less covered with 

 alluvial formations, filled with shells and other 

 productions of the sea. 



The most celebrated of the unknown species 

 belonging to known genera, or to genera nearly al- 

 lied to those that are known, as the fossil elephant, 

 rhinoceros, hippopotamus, and mastodon, are never 

 found along with the more ancient genera ; but 

 are only contained in alluvial formations, some- 

 times along with sea-shells, and sometimes with 

 fresh-water shells, but never in regular rocky stra- 

 ta. Every thing found along with these species is 

 either, like them, unknown, or at least doubtful. 



Lastly, the bones of species which are appa- 

 rently the same with those that still exist alive, are 

 never found except in the very latest alluvial de- 

 positions, or those which are either formed on 

 the sides of rivers, or on the bottoms of ancient 

 lakes or marshes now dried up, or in the sub- 

 stance of beds of peat, or in the fissures and ca- 



