The Paragenetic Relations of Minerals. 103 



been poured into the cavities at one point, but must have 

 been as it were secreted into them. Where the vesicular 

 rocks are traversed by lodes, it is probable that mineral sub- 

 stances have been transferred from them into the vesicles ; 

 thus, at Annaberg (Saxony), metallic bismuth occurs in the 

 vesicles of a rock near to a lode bearing cobalt, nickel, and 

 bismuth minerals. 



It is, moreover, probable that the segregative attraction of 

 homogeneous particles — which has already been alluded to in 

 speaking of the formation of pyrites, — may have contributed 

 to the formation of minerals in vesicular cavities. 



The green earth so frequently met with in vesicular cavi- 

 ties is most likely a product of decomposition, apparently of 

 a mica, rich in protoxide of iron. 



When aluminous and non-aluminous zeolites occur to- 

 gether, the latter are always the more recent. When non- 

 aluminous zeolites are accompanied by calcite, this is the 

 more recent. 



Although the varieties of felsite, especially sanidine, occur 

 so frequently as essential constituents of amygdaloid rocks, 

 no kind of felsite has ever been met with in a vesicular cavity. 

 But the most frequent aluminous zeolites contain the consti- 

 tuents of felsite plus water, consequently there is great pro- 

 bability that they have been formed, in many instances at 

 least, by the decomposition of felsites. Indeed, desmin, de- 

 cidedly the most recent of these zeolites, has a great crystal- 

 lographic analogy to felsite. 



Zeolites have never been found imbedded in a porphyritic 

 manner in any undecomposed rock, and this circumstance 

 agrees with the view that they have been formed by an ex- 

 traction of the rock by water ; for in such case, the new pro- 

 ducts could only be deposited in the vesicles or tissures. 



The definite successions of minerals in vesicular cavities 

 are the same as those observed upon lodes ; there are, indeed, 

 instances of lodes and vesicular cavities occurring in the same 

 rock, both containing the same minerals and in the same 

 order of succession. 



Among geological phenomena, those presented by lodes 

 are probably second to none in interest, both in a scientific 



