GEOLOGY. 499 



groups ; the first termed Dttuvian, because conjectured to have 

 been formed at the period of the general deluge. In the strata 

 of this description are found remains of the elephant, rhino- 

 ceros, and other large animals. Many of the boulders, or rol- 

 led masses, belong to this formation. 2. Postdiluvian, or those 

 formed since the deluge by the decomposing effects of water and 

 the atmosphere. 



V. VOLCANIC ROCKS. All those rocks which seem to owe 

 their present characters to the action of subterranean heat are 

 termed volcanic. They are divided into true volcanic and pseu- 

 do-volcanic ; the first consisting of masses which have run in 

 streams, or have been projected in the form of dust or small 

 masses from the craters of volcanos in a state of activity, such 

 as lava, tuffa, and volcanic dust ; the second comprehending 

 clays and ironstones, indurated and partially melted by the 

 heat from beds of burning coal. 



Such are the arrangements of the mineral masses which form 

 the surface of the globe, detailed more with the view of classi- 

 fication and nomenclature than as suggesting any theory of their 

 formation. A much greater number of recorded facts is pro- 

 bably necessary to warrant the assumption of general principles 

 applicable to the formation of any class. What is already 

 known leads the mind by steps back to the world's early history, 

 and presents to contemplation a period when no plants or ani- 

 mals were in being, and ages perhaps before man was called 

 into existence, to observe and record. It is satisfactory, how- 

 ever, to find, that the facts observed may all be explained in ac- 

 cordance with the earliest history of the world as preserved in 

 the Sacred Writings; and though it would not invalidate the au- 

 thority of that most venerable volume, should an apparent in- 

 congruity exist between modern physical observation and a 

 narrative dedicated chiefly to man and his moral history, yet the 

 coincidence in most minds will not be without its value in the 

 estimation of rival theories. 



