S58 MINERALOGY OF THE REDHEAI>. 



at the bottom of the vein, is parallel with the 

 sides of the fissure. The sandstone in the veiny 

 is much impregnated with calcareous matter, and 

 even contains interspersed crystals of calcareous- 

 spar. This is a very fine illustration of the theory 

 ef veins. 



This conglomerate, in another place, appears in 

 an unconformable position w^ith regard to the 

 sandstone. A little to the south of the small fish- 

 ing village of Auchmithie, the common sandstone 

 is suddenly intercepted by a vertical vein of Heavy- 

 spar, nearly two feet in breadth ; and on the other 

 side of this vein, the gravelstone appears contain- 

 ing many small beds of sandstone. This conglome- 

 rate, which comes thus suddenly in contact with 

 the sandstone, is seen to be in unconformable posi- 

 tion, as at a little distance it rests its horizontal 

 strata upon the extremities of the more inclined 

 strata of sandstone. Similar appearances in the 

 stratification, are observable in the beds of por- 

 phyry and sandstone to the w^est of Dundee^. 



These two rocks which have now been de- 

 scribed, m.ust be referred to the class of mechani- 

 cal deposits, as the eye is unable to discriminate 

 between the sand and gravel, and the rocks of 

 sandstone and gravelstone, the form and structure 

 of the beds being the same. Viewing them, there- 

 fore, in this light, whence have the materials, and 



* See p. IS9. of this volume. 



