220 LOWEST, OR OLD RED, SANDSTONE. 



graywacke schist is too common to render any exam- 

 ples necessary ; as that with the finer schists must 

 needs be so, where these are intermixed, while occur- 

 ring also where fine clay-slate occupies large indepen- 

 dent tracts, as near Oban and elsewhere. It succeeds 

 micaceous schist, necessarily, on the southern border 

 of the Highlands, because this rock is often, here, the 

 last of the primary series ; while this remark includes 

 the associated chlorite and talcose schists. But I must 

 observe, that at this contact, in some places, the mica- 

 ceous schist passes by an apparently regular gradation 

 into the sandstone, through a conglomerate, formed of 

 its fragments and becoming gradually red ; while the 

 conformability of the two rocks in some places, has 

 led incorrect observers to say that there was no dis- 

 tinction between the primary and secondary classes. It 

 reposes on gneiss very widely in Scotland; and here 

 also the union is often such, that an actual transition 

 between the two rocks has been imagined by similar 

 observers. A more interesting case of its connexion 

 is that with granite, conspicuously displayed, among 

 other places, near the Ord of Caithness. And it is 

 worthy of notice, that at the junction in this place, it 

 is often difficult to distinguish between the two; so 

 perfect is the union, and so nearly alike are the mine- 

 ral characters. The ingredients of the sandstone, at 

 the contact, consisting of granitic fragments, are so 

 compacted, and in soine places, so blended with the 

 granite, that a common eye might easily confound them, 

 and a hypothetical geologist consider this a true gra- 

 dation between these rocks; especially as the lowest 

 strata of shale and sandstone also, are so united with 

 the granite as to give the fallacious appearance of con- 

 tinuity. If I have not hitherto observed the sequences 

 of this sandstone to quartz rock, it must be from want 



