Sandstone in the County qf Forfar. 117 



The whole mass of serpentine which I have now described 

 on the left bank, is ninety yards in thickness. It is not stra- 

 tified, but is shistose on the great scale, dividing, with some 

 degree of regularity, into slabs, if so they may be termed, 

 about two feet in thickness, which are parallel to the sides of 

 the dike, and which are again divided into flattish masses, 

 with wedge-shaped terminations. The direction of the dike is 

 about E. and W., and it is nearly vertical, but with a slight 

 inclination to the W. Where the sandstone and slate, which 

 I have already mentioned, join the eastern extremity of the dike, 

 there is a small interval of decomposed serpentine ; but the 

 strata are nevertheless distinctly seen to dip away from the 

 vertical serpentine at an angle of fifty, and, like those on the 

 western side, they are inclined towards the S. S. E. The 

 slaty sandstone is here soft and ferruginous, but it does not 

 present any decided indications of being altered by the con- 

 tact of the serpentine. Next follows a vertical mass of rock, 

 unconformable to the last mentioned sandstone. It is seven 

 yards or more in thickness, and consists of an indurated sili- 

 ceous sandstone, much iron-shot, and containing a few quart- 

 zose pebbles much charged with iron. The sandstone is tra- 

 versed by veins of brown spar. Its fracture approaches to 

 conchoidal, and it has every appearance of being an altered 

 rock. In contact with this mass on the other side, serpentine 

 again appears, differing from that which constitutes the great 

 dike from which it is separated by the strata of sandstone and 

 conglomerate already described. This rock is composed of 

 green serpentine and white magnesian carbonate, the latter in 

 smaller proportion. These are blended together so as to form 

 an irregularly striped rock. 



This serpentine is only a foot and a half in thickness, but 

 it appears to have belonged to a mass twenty-five yards or 

 more in thickness, and which has decomposed and left an in- 

 terruption, at the further extremity of which the serpentine 

 again is seen, having all the same characters, and containing 

 small crystals of quartz of the usual form. On the opposite 

 bank, the soil clearly indicates the decomposition of a similar 

 serpentine, but it has extended there much farther towards 

 the great dike, and may even be connected with it. On that 



