294 FOSSIL GEOLOGY OF UNIT ED STATES. 



In forming a correct idea of the mode of petrifac- 

 tion, we must bear in mind that rock strata are very 

 generally permeiitcd by water charged with minute 

 portions of calcareous, silicious, and other earths 

 in solution ; for we have already seen that water is 

 capable of dissolving mineral substances to a con- 

 siderable extent. When an animal or vegetable is 

 left exposed to the open air, it putrefies and is de- 

 composed into its original elements, oxygen, hydro- 

 gen, and carbon, which escape into the air or are 

 washed away by the rain, so that all vestiges of 

 tliem shortly disappear. Suppose, now, that they 

 aie buried in the earth, they will decompose, of 

 c( urse, more gradually; and, as fast as each particle 

 is set free by decomposition, its place will be filled 

 with particles of mineral matter, such as lime, or 

 flint, or clay. In this way a cast of the interior of 

 certain vessels may be taken, and afterward the 

 walls of the same may decay and sulfer a like trans- 

 mutation. But jwhen the whole is changed into 

 stone, it may not form one homogeneous mass of 

 stone or metal ; for either some of the original 

 woody or bony matter may remain mingled in cer- 

 tain parts, or, what is more often the case, the min- 

 eral which is deposited may be so crystallized in 

 different parts as to reflect light difi^erently, and 

 thus exhibit the exact texture of the original body. 

 For example, Prof. Goppert, of Breslau, steeped a 

 variety of animal and vegetable substances in water, 

 some holding silicious, others calcareous, others 

 metallic matter in solution. He found that in the 

 period of a few weeks, or even days, the original 

 bodies thus immersed were mineralized to a certain 

 extent. Thus, then, vertical slices of deal, taken 

 from the Scotch fir, w^ere immersed in a moder- 

 ately strong solution of sulphate of iron. When 

 they had been thoroughly soaked in the liquid for 

 several days, they were dried and exposed to a red 

 heat until the vegetable matter was burned up, and 



