216 LOWEST, OR OLD RED, SANDSTONE. 



stone is as compact and pure as quartz rock, the land 

 is often as barren as upon this worst of all subsoils. 



The position of the strata presents every possible 

 variety ; being nearly horizontal in Orkney, in Caith- 

 ness, and in many parts of the middle and southern 

 districts of Scotland ; while, in other places, it occu- 

 pies every angle between the horizontal and the ver- 

 tical, as may be seen on the southern boundary of the 

 Highlands, in Invernessshire, and in Shetland. In 

 Arran, the beds are bent into convex forms or more 

 complicated curves ; while examples of simple curva- 

 tures, or of more extensive undulations, occur in nu- 

 merous other places. The tendency of the dip is ex- 

 tremely uncertain ; respecting, in some place or other, 

 every point of the compass ; while the general north- 

 easterly direction of the primary strata of Scotland, 

 ceases to be traced in this one. 



Though an unconformable position to the primary 

 strata has often been held a necessary character of 

 the secondary, this rock is conformable to the conter- 

 minous ones, at many points on the southern boundary 

 of the Highlands and in Arran. The examples of re- 

 verse position are too numerous to require specifica- 

 tion. There is indeed no reason why it should not 

 lie in every possible position with respect to these ; as 

 formerly indicated, \vhen treating of this subject. In 

 Shetland and other places, there occur instructive ex- 

 amples of the mode of junction between the superin- 

 cumbent sandstone and the primary rocks ; the cavi- 

 ties in the irregular surfaces of the inferior set being 

 filled with a conglomerate, without marks of stratifi- 

 cation, and resembling an accidental heap of rubbish, 

 which, as it proceeds upwards, gradually assumes the 

 stratified character ; till a regular series of strata is 

 the result ; while thev become unconfbniiabie to the 



