190 THE NATURALIST IN NICARAGUA. [Ck. VI. 



the normal arrangement of the minerals is very different. 

 The deposition of various spars one on the other in cavities 

 is a secondary operation ever now going on, and has 

 nothing necessarily to do with the original filling of the 

 lodes ; indeed, their arrangement is so different that it 

 helps to prove they have been differently formed. 



It would take a volume to discuss this question in all 

 its bearings, and as I have already entered more fully 

 into it in another place,* I shall only now give a brief 

 resume of the conclusions I have arrived at respecting the 

 origin of mineral veins. 



1. Sedimentary strata have been carried down, by 

 movements of the earth's crust, far below the surface, 

 covered with other strata, and subjected to great heat, 

 which, aided by the water contained in the rocks and 

 various chemical reactions, has effected a re-arrangement 

 of the mineral contents of the strata, so that by mole- 

 cular movements the metamorphic crystalline rocks, 

 including interstratified granites and greenstones, have 

 been formed. 



2. Carried to greater depths and subjected to more 

 intense heat, the strata have been completely fused, and 

 the liquid or pasty mass, including the contorted strata 

 above it, has formed perfectly crystalline intrusive granites 

 and greenstones. 



3. As the heated rocks cooled from their highest parts 

 downwards, cracks or fissures have been formed in them 

 by contraction, and these have been filled from the still 

 fluid mass below. At the beginning these injections 

 have been the same as the first massive intrusive rocks, 



* Mineral Veins," by Thomas Belt John Weale, 1SG1. 



