184 GEOLOGY OF ARRAN. 



sandstone rock, which dips nearly S.W. The depth is 

 about fifteen feet in the lower part, but the upper surface 

 declines southwards, or down the burn, so that the bed 

 becomes thicker upwards. The clay is excessively hard 

 and tough, and the hammer makes no impression upon it ; 

 the imbedded stones are of all sizes, from small pebbles 

 to large boulders, all confusedly mixed, and many striated, 

 smoothed, or polished. It is very striking to observe the 

 prevalent rounding-off upon the edges of a large proportion 

 of the stones, and the high polish which has been given to 

 them, and that upon all alike, of whatever size. This seems 

 clearly to indicate a powerful agent acting for a long period. 

 It cannot have been a continued transport in water, for, as 

 already observed (Art. 22), this action would have left no 

 trace of striation. The majority are local, but comparatively 

 few of sandstone; porphyry, greenstone, and syenite, which 

 form the higher grounds and the hills northwards, abound, 

 but there is also granite of the coarse-grained or Goatfell 

 variety, and slate, both, of course, from the northern moun- 

 tains. The ordinary wash covers, in most places, the surface 

 of the boulder-clay, and in this wash adhering to the surface, 

 we found a few small fragments of shells; no fragment in 

 the clay itself. Over this is a clay bed, the repository of the 

 shells, sinking southwards with the upper surface of the bed 

 below. It is seven to eight feet thick, and is a hard 

 compact, rather fine and dark clay, with a good many 

 small stones, not striated as a whole ; our experience, indeed, 

 is, that few were striated. The deposit is very different 

 from that below; much less compact, more easily worked, 

 and the contrast of the stones is remarkable. The upper 

 part of the bed is of a reddish colour, and a little sandy? 

 while, in the lower part, the colour has more of a bluish 

 tinge, like the boulder-clay, shewing that it was formed on 

 the spot, and partly out of the boulder-clay, on the bottom 

 where the shells were living. The arctic character of this 

 bed is clearly shewn by two of the s}>ecies found in it 



