102 THE NATURALIST IN NICARAGUA. [Ch. VI. 



stones of calcite derived from neighbouring beds of lime- 

 stone, and some minerals derived from a previous igneous 

 injection; and crevices and cavities, called rag/is by the 

 miners, have been filled more or less completely with 

 crystals of fluor spar, quartz, and various ores of metals 

 from true aqueous solutions, or by the action of super- 

 heated steam. 



6. By these 'means the signs of the original filling of 

 many mineral lodes, especially those of the baser metals, 

 have been obscured or obliterated ; but in auriferous 

 quartz lodes both the metal and the veinstone have 

 generally resisted all these secondary agencies, and are 

 presented to us much the same as they were first deposited, 

 excepting that the associated minerals have been altered, 

 and in some cases new ones introduced, by the passage of 

 hot springs from below or percolation of water from the 

 surface. 



