Mr. Napier on Mineral VehiK and Water- Worn Stones. 235 



nesia, might pass off with the remaining water. Many whinstones con- 

 tain a great quantity of lime as a component, which makes this reaction 

 more certain ; and veins of calc spar are abundant in the trap rock — a 

 specimen taken within a few inches from a vein of spar, contained 9 per 

 cent, of lime. 



The change by water is not confined to the trap rock. We have here 

 a boulder of bastard limestone, completely changed in its character for 

 several inches deep, so as to give no idea of its original appearance by 

 external observation. The following is the nature of the change : — 



Altered Part. 



Silica 28-4 



Carbonate of lime 3 6 



Peroxide iron 40*5 



Carbonate of magnesia 1'4 



Kernel 



Silica 12-2 



Carbonate of lime 22*5 



Carbonate of iron 42-8 



Carbonate of magnesia 12 "4 



Sulphur 1-1 



Water 84 



99-5 



Sulphur 3'5 



Water 21-3 



98-7 



Thus the same class of change has taken place, as with the trap, lime 

 and magnesia has dissolved, and the iron, peroxidised, has lost its car- 

 bonic acid. We have occasionally found stones in the gravel deposit that 

 apparently have been broken in two, and the two halves lying very 

 close to each other, have received a deposition of minerals between them, 

 so as occasionally to cement the two parts together at the points closest 

 to each other, such as in the sample present— this sample stone before 

 you, which is composed of 



Insoluble matter GO'S 



Protoxide of iron 22*5 



Carbonate of lime 6"6 



Magnesia O'S 



Sulphur 2-5 



Loss at red heat 6G 



99-5 



The three minerals filling up this fracture, namely, sulphur, iron, and 

 carbonate of lime, are also, we observe, component parts of this stone, 

 but we would not venture to say that the stone is the source of these 

 minerals, neither would we assert that the deposition of these minerals 

 has taken place in the alluvial deposit in the position in which the stone 

 was found,— the question suggesting itself being, why the crystallization 

 only goes on in the fracture, and not upon any other part of the stone. 

 Should these mineral depositions be found to take place in such stones in 

 their position as bouhlcrs, it will show, what we believe to be the case, 

 that tliere is some influence effecting mineral depositions in veins or 

 fractures, or even in the fragment of a rock, when these are placed in 



