234 Mr. Napieb on Mineral Veins and Water- Worn Stoneg. 



As the formation of many of these minerals may depend upon causes 

 constantly in operation, I have thought it possible that indications of 

 these might be obtained in detached stones, found m the alhivial deposits. 

 My search into these have been, as yet, limited, but by dravring the 

 attention of the members of the Society to the subject, more extensive 

 observations may be made, and either the utility, or futility, of the 

 research manifested. 



In some of the loose stones found in the alluvial bed, are seen changes 

 that have evidently taken place since they were detached from the rock, 

 and analogous to those changes that are taking place in the rock. 



The first changes I refer to are well known ; it is, that water in contact 

 with, and passing through, ro^ks, changes the character of these, by 

 dissolving out some of their component minerals. A piece of trap rock, 

 for example, exposed to water, very soon changes, when alternately wet 

 and dry, and exposed to the atmosphere ; the decomposition is sensibly 

 apparent, a brown crust is soon formed, which becomes soft and brittle, 

 breaking off by slight friction, leaving a new portion of the stone to 

 undergo the same change. The same sort of stone imbedded in the 

 gravel under the soil, passes through the same changes, but the crust, in 

 this case, is not so soft and brittle ; the change soon penetrates to the 

 centre of the stone, giving it a different character and appearance. 

 Analysis of the stone so changed, compared with the original, makes the 

 change very apparent. We^ give the average of many analyses, from 

 different localities : — 



Kernel, or Original Crust, or Altered 



Stone. Stone. 



Insoluble matter, 72*5 



Peroxide of Iron, 19.7 — f«i8 3 



Lime 09 



Magnesia, 0"3 



Potash, trace 



Loss at red heat, 5*8 



99-2 



Insoluble Silicate of 



Alumina, 66"8 



Protoxide of Iron, 18-5 — i 



Lime, 3"8 



Magnesia, 1"5 



Potash, 2-6 



Loss at red heat water, 6'2 



99-4 



Here, then, we find that water has dissolved out, lime, iron, magnesia, 

 and potash, and the remaining iron changed to the peroxide state. The 

 length of time required for the water to penetrate a piece of trap I know 

 not, but that the soluble power of the water is great, is evident, by 

 placing a piece of such rock in distiUed water; 100 grains digested for 

 6 days, at summer heat, lost one per cent., the water had an alkaline 

 reaction, and contained magnesia, potash, and lime. Now, if a crack or 

 fissure existed in such a rock, and water oozed through, which it does, 

 more or less, in all rocks, the crack would unavoidably get filled with 

 lime in a state less or more crystalline, according to circumstances, lime 

 being much less soluble in water, while the potash, and probably mag- 



