IN THE SOUTH OF ARRAN. 527 



Three — Pecten islandicus, Astarte arctica, and Cryptodon Sarsii (if it be really 

 distinct from the sinuosum)., are distinctively arctic, a character further indicated 

 forthe whole collection by the prevalence of astartes, which, both in species and 

 individuals, greatly outnumber all others. 



Vegetable remains, apparently heather stalks, were present at two places in 

 the boulder-clay. 



In general, the material of the boulder- clay is derived from the rocks of the 

 particular glen in which it lies. Still foreign materials are not wanting. Thus, 

 in Cloinoid Glen, I found pieces of syenite, which must have crossed the water- 

 shed between that glen and the Torlin Glen to the east, in which the syenite 

 rock lies. In the same glen also were pieces of a very peculiar (carboniferous) 

 sandstone, which must have come down across two water-sheds, from the Clachan 

 Glen to the north. Fragments, too, have been brought down from the Silurian 

 shales in the north-west, and from the granite in the north ; and one bit of impure 

 coal I found, which must have come either from the little patch of coal in the ex- 

 treme north-east, or from the mainland opposite. All these wanderers have pro- 

 bably been brought by floating-ice. 



The red colour of the boulder-clay shows how largely it is indebted to the 

 friable red shales of the district. Hardened knots of this shale, which are always 

 striated, are frequent ; but by far the largest proportion of the stones which it 

 contains are derived from the igneous rocks. The soft laminated felstone, in- 

 deed, which prevails in the south is not common, from its proneness to disinte- 

 gration, but felstone porphyry and greenstones abound. The absence of striations 

 on the stones from the felstone porphyry is very striking. This, how^ever, is 

 apparently due merely to the texture and colour of the stones, and is equally true 

 of the whitey coarse-grained variety of greenstone. 



At the lower levels the surface of the underlying rock is rarely to be seen 

 striated, a fact partly owing to its texture, which is very soft and friable, and 

 partly to the difficulty of getting a surface at once sufficiently exposed, clean, and 

 un weathered. On the shore between Brodick and Lam lash, however, there are 

 some very well-marked striated surfaces. 



I have made these general remarks as full as possible, in order to avoid repe- 

 tition in detail of features common to the whole boulder clay, and will therefore 

 iaow only refer to individual places, in so far as they strikingly illustrate previous 

 statements, or otherwise present something peculiar. 



Below the bridge over the Auchinreach Burn, above Whiting Bay, 70 feet 

 above the sea, the boulder-clay is 40 feet deep. It rests directly on a bed of 

 friable shales. The stones in it are much striated ; small granite boulders aie 

 frequent. At 50 feet above the sea this bank is 50 feet high, but it is only the 

 lower 15 feet that are boulder-clay. The underlying rock is not seen here. The 



VOL. XXIII. PART III. 7 D 



