QUARTZ ROCK. 179 



nexion between the recent coarse shales and the sand- 

 stones to which they belong. The whole of the 

 association, indeed, between quartz rock and argilla- 

 ceous schist, bears a striking resemblance to that be- 

 tween shale and sandstone in the secondary class. Of 

 the connexion between quartz rock and the primary 

 red sandstone I must speak immediately. 



The external character which quartz rock gives to 

 a country, and particularly to the mountains com- 

 posed of it, is generally remarkable., and leads to its 

 detection, even at a distance. Such hills are com- 

 monly of a conoidal shape ; and, under any form, are 

 bounded by a smooth flowing outline, rarely dis- 

 turbed by the asperities so generally characteristic of 

 micaceous schist. They are commonly also covered, 

 on the steeper parts, with fragments, on which no soil 

 accumulates ; their naked whiteness being seldom 

 concealed, even by the growth of a lichen. From this 

 whiteness, often so dazzling in the sunshine as to 

 emulate the effect of snow, the composition of these 

 mountains can often be conjectured at a distance. Al- 

 though these ruins bespeak the degradation of the 

 strata, the disintegration of the rock itself is every- 

 where scanty ; the soil being consequently thin, and 

 consisting of little else than sand mixed with a portion 

 of the black earth of vegetables. Hence they form 

 the most sterile of all the soils of Scotland ; while the 

 same character appears to belong to this rock 

 wherever it has been observed. 



The theory of quartz rock is sufficiently obvious. 

 Its regularity of stratification bespeaks its aqueous 

 deposition, as does its mechanical structure in the 

 cases already described. Where this structure is com- 

 bined with a chemical or crystalline texture, we have 

 only the same difficulties to contend with as in the 



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