176 GEOLOGY OF ARE AX. 



ducts, if order there be. Sandstones, shales, and marls 

 occupy the shore, and stretch far up the river-courses and 

 lower parts of the glens, whose higher sides exhibit in section 

 the series of traps and felstones just alluded to. It would 

 be desirable to have all the strata thoroughly examined for 

 fossils, as these, if found, would fix the age of the beds. 

 These interior sections are more deserving of inspection than 

 the shore, which shews only a repetition of appearances with 

 which we are familiar dikes of greenstone, claystone, and 

 rarely pitchstone, some of the dikes standing up like walls, 

 and numerous granite boulders of moderate size. There are 

 in all about forty dikes, and the range is generally a little 

 "VV. of N. One of the largest is that near Kildonan, forming 

 the little harbour of Drum-la-borra. A dike attaches Pladda 

 islet to the mainland, and has suffered so little disintegration 



* 



in this exposed situation that at high water a vessel can cross 

 only at one place. 



Auchinhew streamlet comes down opposite to Pladda, and 

 shews some fine sections, and a very singular and highly 

 romantic waterfall and pool called Eais-a-Mhor, or the great 

 fall. The fall is N.E. of the Auchinhew farm-house, N. of 

 the road; but the section lower down should first be visited. 

 There are here several alternations of columnar trap and 

 amorphous trap, with sandstone and marl. The horizontal 

 joints and vertical seams are both very distinct, and mark off 

 most of the pillars as pentagonal prisms. At the fall the 

 water descends through a height of seventy or eighty feet into 

 a large circular basin, or amphitheatre, the perpendicular 

 sides of which present a facade of pillars resting on 

 sandstone. Over this is another bed of sandstone, sur- 

 mounted by beds of amorphous trap, which forms the channel 

 of the burn above, towards the moors, and by its hardness 

 has prevented disintegration farther up. The front of the 

 fall is formed by a dike, which, when it reaches the basaltic 

 stratum, divides into two branches and terminates, thus 

 clearly shewing that it formed the vent of eruption. The 



