the Fonnalion of tlte superficial Part of the Gluhe. A'}'> 



to the growth of animals whose coverings contain so much cal- 

 careous matter. Nor is it necessary to suppose that the^e 

 aqueous eruptions were always sudden, and attended with vio- 

 lent convulsions ; for, when a passage was once opened, they 

 may have risen slowly and been diffused in a tratiquil state, and 

 by gradual condensation may have enveloped the most delicate 

 animals or vegetables without injuring their external form. 



The long intervals of repose between the great igneous vol- 

 canic eruptions may have allowed time for the growth and decay 

 ©f animals whose remains are found in different strata ; whilst 

 the formation of other strata may have taken place, under cir- 

 cumstances incompatible with organic existence : and accordingly 

 we find in the rocks most abounding with organic remains, cer- 

 tain strata in which they never or rarely occur. The same agent 

 which enveloped living animals in mineral matter without in- 

 juring their external form, appears in some instances to have 

 immediately arrested the functions of vitality. Petrified fish 

 have been discovered in solid rocks in the very attitude of seizing 

 and swallowing their prey. A sudden eruption of a hot fluid 

 saturated with the different earths (or the elements of whicli 

 these earths are formed) might destroy in a moment the animals 

 previously existing, and form round them a siliceous or cal- 

 careous increstatioQ which would proteet their remains from 

 further destruction. 



Ages of tranquillity might elapse in the iiiter\'al of different 

 eruptions, and beds of gravel and breccia be formed by the gra- 

 dual disintegration of the higher parts of the earth. These beds 

 might be afterwards covered by, or intermixtwith, the crystalline 

 heds from subsequent eruptions :; and may we not in this manner 

 explain the alternation er intermixture of crystalline rocks with 

 those of mechanical formation ? Dislocations of the strata by 

 earthquakes and other causes might also take place between the 

 periods of different formations, in which case the upper beds 

 would rest on the subjacent ones in an unconformable position. 



As the strata which cover each other are often composed of 

 very different mineral substances, may we not inter that the suc- 

 cessive ancient eruptions, whether igneous ox acjueous, contained 

 different elementary parts ? At tlie present day, the lavas of 

 succeeding eruptions even from the same crater differ both in 

 ■external character and eonstituent parts, ileucfi we may ex- 

 plain the formatiou of strata of ironstone and beds of other me- 

 tallic ores alternating with earthy strata ; and we can have little 

 difficulty in the admission, as -it is now known that the bases of 

 the earthy strata are also metallic. Two or more mineral sub- 

 stances may in some instances have been contained in rlic same 

 iluid^ and ^icuaratcd into different masses or strata I>v the laws 



J- f 4 of 



