ART. 12, SIDERITE AND ASSOCIATED MINERALS—SHANNON. 19 
situations of the original or first-generation siderite from over a 
much wider area. Some change must have taken place in the solu- 
tions, since it is difficult to conceive solutions depositing ferric-iron 
opal and ferrous carbonate under the same conditions. The other 
minerals, aside from the hyalite, are very local and more or less 
adventive substances whose source must remain problematic. The 
limonite and goethite are distinct from the other minerals in that 
they are products of ordinary weathering. 
