;34 GEOLOGY OF THE LOTHIANS. 



and greenstone of the Crags (PI. VI. Fig. 2,), it must con- 

 sequently be the product of an eruption posterior to that of 

 the Crags. It runs in an uninterrupted course through the 

 various rocks, and alters the sandstone both in position and 

 mineral structure. As it approaches the greenstone which 

 it traverses, this greenstone passes gradually into a more com- 

 pact variety, an appearance which is not of difficult ex- 

 planation, if we consider that, when in a fluid state, this 

 vein was in contact with previously consolidated rocks. 



After leaving this point, there is a beautiful display of 

 the stratified rocks of the hill underlying the trap. These 

 strata are various alternations of argillaceous sandstone, 

 a brick-red calcareous clay-ironstone, and variously tinted 

 slate-clays, all of which are arranged in perfect parallelism. 

 These occur for a considerable way, till at last they are cut 

 off by a great vertical vein of greenstone. It does not traverse 

 as the other the overlying greenstone, but appears to have 

 been one of the openings through which the protrusion 

 of the trap has been effected. It is about twenty yards broad, 

 and, when next the several rocks, produces alterations, and 

 assumes at its planes of contact a compact structure. Near 

 the northern extremity of the Crags, a vein of a highly fel- 

 spathic uncrystalline greenstone issues from the principal 

 greenstone mass, and traverses the sandstone parallel to its 

 direction. It is about twenty feet long, and at its origin 

 two feet broad. At the northern extremity of the hill, the 

 greenstone sinks rapidly below the plain at the back of the 

 Palace of Holyrood, and is covered by an assemblage of 

 strata similar to those on which it lies. (Plate VI. Fig. 1.) 

 These strata, lying upon the greenstone, occur more or less 

 interruptedly throughout the whole extent of the hill, and 

 the same changes which the greenstone effects upon the 

 sandstone strata at the foot of the trap escarpment, are 



