48 GEOLOGY OF AGRICULTURE. ^ 



are therefore said to be unstratified. The proof is very 

 complete, though it cannot be given here, that the "un- 

 stratified rocks were formed by fire, and that they 

 took the form in which they appear by cooling off 

 after being intensely heated. For this reason geolo- 

 gists have called them igneous rocks ; and, because 

 some portions of them have a crystallized appearance, 

 they are often called crystalline rocks. We have then 

 a class of rocks called indifferently unstratified^ igneous^ 

 and sometimes crystalline^ rocks, whose origin evi- 

 dently was by fire. 



70. It is, perhaps, equally well proved, and is, be- 

 sides, a dictate of common sense, that the stratified 

 rocks must have received their present form by depo- 

 sition from water. For this reason they are often 

 called aqueous rocks, and because most of them con- 

 tain fossil remains of plants and animals, they are also 

 called fossiliferous rocks. 



71. If you were to see, on a steamboat, a row of 

 huge casks, then above them a row of boxes, above 

 these a row of bags, and above all, baskets, bundles, 

 and umbrellas, you would have no hesitation in 

 deciding which had been put there first. No one 

 would dream that the pile had been commenced at the 

 top and built downwards. The casks must have been 

 rolled in first, the boxes placed on them, then the bags, 

 and last of all the lighter matters. Equally clear are 

 the reasonings of geologists. The lower rocks are 

 older ; and the higher are newer, with some excep- 

 tions, to be explained hereafter. 



