536 REV. R. B. WATSON ON THE GREAT DRIFT-BEDS WITH SHELLS 



of very coarse big stones and gravel, much water-worn, and over this 30 to 40 

 feet of boulder-clay ; the materials of which are less coherent than in any of the 

 other glens I examined, having less clay and more stones than elsewhere, and this 

 is a characteristic of the boulder-clay throughout the whole Clachan Glen, a 

 peculiarity obviously due to certain specialities of the valley itself, affecting the 

 disposition of the boulder-clay. 



At 20 feet above this section, the beds are again well shown ; and there the 

 great bed of clay is either buried under the talus of debris, or is absent altogether. 

 At this point a prodigious stretch of the banks is displayed, but too much ruined 

 to aflford much information. Most of the stones are much water-rolled, but 

 many of them still retain traces of striation. By far the greatest number of these 

 are greenstone and felstone porphyry, but the latter, as usual, scarcely ever show 

 striations. Out of 105 stones distinctly striated, which I counted in this bank, 

 there were, — 



Greenstone, ..... 



Knots from the soft red shale. 



Laminated felstone, .... 



Felstone porphyry, .... 



Soft sandstone, ..... 



Green conglomerate, from the altered carLoiiiferons strata, 



Hard, purply, flinty, slatey shale, 



Syenite, ...... 



105 100 



About two miles above the bridge, at 300 feet or so above the sea, is a deep 

 narrow gorge in the valley, where the drift banks are enormous, rising 200 feet 

 high. The gorge is formed by a great felstone dyke, and the shales which it 

 has protected. These have made a kind of dam across the mouth of the upper 

 valley. Both the felstone and the shales crop out in the boulder-clay banks on 

 the south side of the burn, at various points, at 100 or 120 feet above the burn. 

 The shales seem to be overlaid by a mass of laminated or banded felstone, which 

 apparently has spread out from the dyke. This is best seen in a precipice on the 

 south side of the gorge. The greatest mass of boulder-clay lies on the north side; 

 and the top of the bank here, for 8 feet, looks like water-sorted clay and sand, 

 beneath which are some large stones, and below this is boulder-clay. The 

 boulder-clay banks extend up both the main valley and a side branch, which opens 

 to the south-east, above the gorge ; but they lose tliere the huge proportions they 

 have below. 



Before concluding this examination of these beds, I think it may be well to 

 explain why I have so definitely spoken of them throughout, as being composed 

 of boulder-clay. Of course, I am aware that exception may be taken to this 

 application of the name, on the ground that these beds present traces of stratifi- 

 cation, and contain shells. But this objection could at most only apply to the 



28 



= 



27 



per cent 



28 



= 



26 





4 



= 



4 





3 



= 



3 





19 



= 



18 





9 



=: 



9 





9 



= 



8 





5 



= 



5 





I 



I 



