GEOLOGY OF AGRICULTORE. 



RELATIVE AGE OF ROCKS. 



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72. No man in his senses, and with any knowledge 

 of the facts bearing on the question, would contend 

 that the igneous and the aqueous rocks were formed 

 at the same time. Either the heat, requisite to form 

 the igneous rocks, would have -expelled the water ne- 

 cessary to form the aqueous ; or the water, necessary to 

 form the aqueous, would have overcome the heat re- 

 quisite to form the igneous. As well might you tell 

 me that one piece of beef will bake and another 

 freeze in the same oven and at the same time, or that 

 the heat that will melt rocks will not convert water 

 into steam. I would sooner believe either of these 

 things than believe that the upper igneous and the 

 lower aqueous rocks were formed at the same period. 

 In the first place, it seems impossible that this could 

 have been done, as much so as that the same oven 

 could bake and freeze at the same time. In the second 

 place, the aqueous rocks, with a few exceptions, easily 

 accounted for, always lie above the igneous, showing 

 thereby that they were deposited last. And in the 

 third place, the aqueous rocks were manifestly formed 

 out of the igneous, and therefore must have been 

 formed subsequently. If a horse-shoe is made of iron, 

 the iron must have been made first. Such are the 

 reasonings of geologists with regard to the relative 

 age of rocks, and those who doubt their main conclu- 

 sions are generally those who have looked little at the 

 facts. 



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