THE OLD RED SANDSTONE. 145 
polygonal form by pressing against each other, and by the 
weight from above. (See Note [.) 
The gray fissile bed in which these organisms occur was 
perforated to its base on two several occasions, and in different 
parts of the quarries—in one instance, merely to ascertain 
its depth ; in the other, in the course of excavating a tunnel. 
In the one case it was found to rest on a bed of trap, which 
seemed to have insinuated itself among the strata with as little 
disturbance, and which lay nearly as conformably to them as 
the greenstone bed of Salisbury Crags does to the alternating 
sandstones and clays which both underlie and overtop it. In 
the other instance the excavators arrived at a red, aluminous 
sandstone, veined by a purplish-colored oxide of iron. The 
upper strata of the quarry are overlaid by a thick bed of 
grayish-red conglomerate. 
Leaving behind us the quarries of Carmylie, we descend the 
hill-side, and rise in the system as we lower our level and 
advance upon the sea. For a very considerable distance we 
find the rock covered up by a deep-red diluvial clay, largely 
charged with water-worn boulders, chiefly of the older pri- 
mary rocks, and of the sandstone underneath. ‘The soil on 
the higher grounds is moory and barren—a consequence, 
in great part, of a hard, ferruginous pan, which interposes 
like a paved floor between the diluvium and the upper mould, 
and which prevents the roots of the vegetation from striking 
downwards into the tenacious subsoil. From its impervious 
character, too, it has the effect of rendering the surface a bog 
for one half the year, and an arid, sun-baked waste for the 
other. It seems not improbable that the heaths which must 
have grown and decayed on these heights for many ages, may 
have been main agents in the formation of this pavement ot 
barrenness. Of all plants, they are said to contain most iron 
15 
