MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 471 



rounded pebbles, both from the greywacke and felspathic rocks, were formed ; and 

 beyond, as well as above these conglomerate beds, strata of sand and mud were 

 deposited in greater or less abundance. 



In regard to the deep red colour by which these conglomerate and other sedi- 

 mentary beds are characterized, it is pretty plain that it has been derived in some 

 way or other from the greywacke formation. That the red oxide of iron (in the 

 state of a peroxide) prevails largely among the greywacke strata, both in the 

 form of veins of hematite, and diffused through the substance of the rock, has 

 been already shewn. The disintegration, therefore, of these rocks, would produce 

 extensive beds, impregnated with iron ; and as such a sediment would be heavier 

 than pure sand or clay, the beds formed by it would be mostly deposited in the 

 immediate neighbourhood of the greywacke hills. 



This last inference is proved to be correct from this circumstance, that the 

 red sandstone strata are most abundantly developed, and most deeply tinged along 

 the flanks of the hills. It is at a considerable distance from them, that we find the 

 yellow and white beds of sandstone beginning to make their appearance ; and it 

 is still farther off, before we reach the shales, marls, and sandstones of the coal- 

 measures, which present little or no intermixture of iron-shot strata. 



This seems to be the most proper place for adverting to the probable origin 

 of those white spots and blotches which are occasionally seen in the old red sand- 

 stone formation. Dr FLEMING has suggested that they are owing to the presence 

 " probably of some vegetable or animal organism, the decomposition of which ex- 

 ercised a limited influence on the colouring matter of the surrounding rock." 



Being desirous of testing, by chemical analysis, the soundness of this expla- 

 nation, I requested my friend Dr MADDEN of Pennicuick to do me the favour to 

 examine one of those white spheres, and at the same time a portion of the red 

 stone adjoining it. This experiment he very readily undertook, and the following 

 is the result. 



In Spot. In Red Sandstone. 



Silica, . . 67.4 .. 63.40 



Alumina, . . 



Carbonate of lime, . . 



Iron, 



Phosphate of iron and alumina, 



Alkalies, 



Moisture and loss, 



100. 100. 



Dr MADDEN, in sending this analysis to me, observes, that, " although it does 

 not shew the difference to be so great as I at first imagined, still I should think, 

 from the result, that some powerful de-oxidizing agent had been at work, as it 

 has so completely changed the condition of the iron. In fact, both this and the 



