472 MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 



alumina were in the spot in some curious condition, rendering them very diffi- 

 cult to separate, so that probably their numbers are not so correct as they 

 might be." 



From the foregoing analysis, it appears (1.), that there is in the spot treble 

 the quantity of alumina which is in the adjoining red stone; (2.) that there is in 

 the spot, less than half the quantity of iron which is in the red stone ; (3.) that 

 the iron in the spot is in the state of a protoxide, whilst in the red stone it is a 

 peroxide ; and, (4.) that there is phosphoric acid in the spot, whilst there is none 

 in the stone. 



There are two ways of accounting for the difference between the spot and 

 the red sandstone. The peroxide of iron, which prevails through the general 

 mass of the rock, may never have impregnated the white spot, owing to the 

 presence in it of some body which had the power of repelling it ; or the per- 

 oxide of iron may have subsequently, as Dr MADDEN suggests, become de- 

 oxidized. 



In reference to this last theory, it may be observed, that if the abstraction of 

 oxygen from the iron be ascribed to the action of some body previously existing 

 in the heart of the stone, does the analysis above given indicate what that body 

 is ? Dr MADDEN infers that there has been " some powerful de-oxidizing agent at 

 work ;" but, as he does not surmise what this agent was, it is to be presumed 

 that he had been unable to discover it. Dr FLEMING, as above mentioned, suggest- 

 ed that the decomposition of animal or vegetable matter might have decolorized 

 the stone ; and, in corroboration of this opinion, I may state, that I am in posses- 

 sion of one specimen, where there is a scale of a Holoptichius in the middle of 

 the white spot. Now, as this scale consists to a great extent of phosphate of lime, 

 it may be supposed, that, on the decay and decomposition of part of the scale, 

 the phosphoric acid would combine with a portion of the iron in the peroxide, 

 and convert it into a protoxide, which is generally of a whitish-grey colour. But 

 whilst in this way the change in the state of the iron may be accounted for, what 

 reason can be given for the other differences between the spot and the stone, 

 the larger supply of alumina in the former, and the smaller quantity of iron ? 



Farther, it is deserving of observation that it is only in one case out of a 

 thousand, that any foreign body is discernible in the white spots. And if it is 

 assumed that a foreign body, such as a fish-scale, be the sole cause of the spot, 

 why should its form not correspond with that of the fish-scale, instead of being an 

 exact sphere, which is the form universally exhibited ? 



I cannot help thinking that the formation of these white spots belongs to the 

 same class of phenomena as the blanching process which takes place along the 

 sides of fissures or cracks in the old red sandstane rock. On each side of the 

 crack there will be found, on breaking off a portion of the rock, to be a ribbon of 

 a greenish- white colour which fringes the red stone. It appears to me that this 



