OEIGIN OF VOLCANIC ROCKS DISCUSSED. 13 



but if you will go to such or such a locahty, — indicating some new one, — 

 you will find an undoubted passage of the sedimentary rock into eruptive 

 forms." When this new locality is also examined and the statements are 

 found to be erroneous, another one is mentioned, and so on; until one must 

 demand hereafter of these observers that they shall select some locality on 

 which the}^ shall be willing to I'uUy and linally stake their pet hj-pothesis, 

 and iibide by the evidence. 



It has been claimed that the results of chemical analysis show that vol- 

 canic rocks are derived from sedimentary ones. While it is true that the 

 former have a composition chemically like some of the latter, this resem- 

 blance is easily explained by the fact that a sedimentary rock ought to 

 resemble chemicallv the massive rock from wliose destruction it came. The 

 chief difference between them would be that resulting from the change 

 brought about by outside influences, the introduction of foreign material, 

 etc. Hence the chemical resemblance between the two classes of rocks 

 can naturally and readily be explained b}- the derivation of the sedimentary 

 from the eruptive rocks ; and there is no need to resort to the unnatural and 

 h3'pothetical derivation of the volcanic from the sedimentary rocks. The 

 former derivation is the one seen to take place everj' day, while the latter 

 is unproved as yet, and those who hold it are apparently looking at the 

 effect, and making it the cause. In other words, it seems to the writer that 

 these observers have taken hold of the subject at the wrong end. 



In examining the products of volcanoes, certain minerals appear to be 

 characteristic of them, which are of prior origin to the consolidation of the 

 lava. These minerals show evidence that a hot magma has directly acted 

 upon them, and every gradation can frequently be seen between the almost 

 untouched mineral, and the nearly destroyed one. 



I regard these minerals, unless they were caught up by the lava during 

 its passage from the earth's interior to its surface, as evidences that the 

 material from which the lava was derived is no longer in its original con- 

 dition, although this condition was not like that of any of our sedimentary 

 rocks. Certain of these minerals are easily destroyed ; two at least, suffer- 

 ing alteration readily on exposure, and it seems impossible that they could 

 survive when the much le.ss perishable materials of our sedimentaiy rocks 

 have been entirely obliterated, if, as is supposed by many, they were ever 

 there. These minerals are unlike, either in species, variety, or form, with 

 possibly a few exceptions, any minerals occurring in sedimentary rooks as a 



