GEOLOGY. 



315 



Different Effects of Combustion and Ignition. 



Bodies exposed to heat in contact with the atmos- 

 phere undergo a chemical change; their more vola- 

 tile parts are driven off, and the inflammable parts 

 combine with oxygen, but in a state of mere ignition; 

 under great pressure, and confined from all access to 

 air, water, &c., the same bodies will remain red-hot 

 for ages without undergoing any change but that of 

 simple fusion, whereas by combustion a chemical 

 change is effected. 



Igneous Origin. 



Rocks known to be the produce of fire may be 

 limited to granite, the trap rocks, and the volcanic 

 rocks. Perhaps gneiss, micaceous schist, and other 

 primary strata, may be added. 



Theory of successive Creations. 



The discovery of animals peculiar to certain for- 

 mations, and the general agreement with each other 

 of the fossils of the same formations, have led to the 

 inference that these several formations were the con- 

 sequences of successive changes effected on the 

 earth's surface, and that their contained fossils are 

 the preserved remains of several creations, which had 

 been successively formed, to accord with the existing 

 condition of the planet under its several changes. 



In the lower and early formed strata are the re- 

 mains of unknown vegetables, and in the mountain 

 limestone accumulations of crinoidal and terebratular 

 remains, which do not now exist, as also multilocular 

 shells, such as ammonites and belemnites, which do 

 not now exist except in the instance of the nautilus. 



The fossils of the next superior formation (the 

 lias), yield strong proofs of their having been the 

 production of a distinct creation, the shells (ostrea, 

 &c.) differing essentially from those of the preceding 



