354 



On Veins. 



[May, 



same rock not parallel to each other; but crossing and cutting 

 through each other at various angles. When that happens, one 

 of the veins always passfes on without interruption, while the 

 other is cut in two, and the parts of it separated from each 

 other. Now it is impossible to avoid concluding, from the 

 whole phenomena of veins, that the rocks in which they occur 

 existed before them. It follows, irresistibly, from the fact just 

 mentioned, that the veins themselves were not formed all at 

 once, but at different periods; and the way in which they cross 

 furnishes us with the key to determine their relative ages. That 

 vein which passes without interruption through another must be 

 newe?' than that other; and the vein which is interrupted, and 

 its parts separated, must be the older of the two. 



7. Every substance has been found in veins, which constitutes 

 a part of all the various rocks composing the crust of the earth. 

 The rocks themselves, each in its turn, fill various veins. On 

 the other hand, every substance hitherto found in veins has been 

 found also in rocks. Hence^^ with respect to constituents, there 

 is no difference between veins and rocks. 



8. All the rocks which constitute the crust of the earth, and 

 which have been described and named by mineralogists, with 

 scarcely a single exception, occur also in veins. Now it deserves 

 particular attention that the veins filled with rocks are just as 

 regular in respect to position as the rocks themselves, with por- 

 tions similar to which they are filled. The order which they 

 observe is this. Every rocky vein (if I may be allowed the 

 expression) occurs in rocks nearer the central nucleus than the 

 formation of which it constitutes a part. Or, in other words, 

 veins filled with a particular formation are always found under 

 that formation, and never above it. Thus in the primitive rocks 

 v/e find veins of transition and fleetz rocks; but in the transition 

 rocks, we never find veins of any primitive formation, but only 

 of transition and Jioetz rocks; and, lastly, in the ^oe/»; formations 

 we never find veins either of primitive or transition rocks, but 

 only of Jioetz rocks. The same invariable rule holds good with 

 respect to the individual formations of all the great classes. 



Farther, when two veins of different formations intersect 

 each other, that v*?hich is filled with the formation nearest the 

 nucleus is always cut through by the other. 



The veins then follow the same invariable order with respect 

 to position that the rocks do, and there is clearly a connection 

 between them ; but we know, from the facts already stated, that 

 the veins must have been formed at different times. Nov/ as the 

 order in which they intersect each other is precisely the order of 

 the position of the different formations, it follows irresistibly 

 that the order of position is iikev/ise the order of the formation 

 of all the different rocks which compose the crust of the earth. 



