IN THE SOUTH OF ARRAN. 535 



Between Glen Scoradale and the Great Black Water Valley there are immense 

 beds of boulder-clay, and also of water-rolled gravels but, I only marked their 

 jjresence without examining them in detail. 



In the Clachan Glen, the great boulder-clay beds extend from the bridge at 

 its mouth at 190 feet above the sea upwards for a mile and a half or two miles. 

 At 220 feet above the sea, felstone rock appears in the burn-course, but it is all so 

 shattered on the surface and buried in debris, that no striations can be seen. At 

 250 feet above the sea, the shales reappear. Here, in the open and flat valley- 

 bottom, a bank rises 20 feet above the burn which presents the section shown in 

 l^late XXII. fig. 14. The lower part is entirely concealed by a talus of debris, 

 above which the shales rise perpendicularly on the left. These are partly over- 

 laid by 2 feet of dense gravel, very hard pressed, which belongs to the boulder- 

 clay series. Above both the shales and the gravel-bed are 3 feet of large loose 

 stones, and 2 feet of fine sand, with earth over all. The two latter beds, that, 

 viz., of stones and that of sand, seemed to me to belong to the class of later 

 superficial deposits thrown down when the boulder-clay was eroded by the action 

 of a lake or bay of the sea. 



A little way behind this on the north, the boulder-clay banks rise 120 feet 

 high, while 100 yards east, or further up the burn, they reach 170 feet. The 

 upper part of this bank consists of hard stratified gravels, less dense than usual 

 in the boulder-clay, and the surface below the turf has three inches of fine hard 

 clayey sand. 



By far the best sections of the drift are to be seen on the other (the south) side 

 of the burn ; for there, though hardly more continuous, they are somewhat more 

 perpendicular and less obscured by debris than on the north side. Unfortunately, 

 however, they are so far obscured and interrupted, that the beds which they 

 jiresent cannot be traced continuously for any distance. At 290 or 300 feet above 

 the sea is certainly the best and most interesting view that can be got of them, the 

 whole bank being cleared from the burn upwards for 90 feet. (Plate XXII. fig. 15.) 



At the bottom is some 15 feet of hard gravelly clay ; above this a layer of 4 or 

 5 feet of great stones and gravel ; then 15 feet of dense finely laminated clay 

 with fine sand, becoming more sandy towards the top. In the uoper part of this, 

 almost at its junction with the overlying bed, I found some small broken twigs of 

 exogenous wood, crushed flat. They were lying well into the bank, between the 

 undisturbed horizontal layers of the sand, and beyond a doubt belonged to the 

 period of the formation of the bank. Next is a bed 8 feet thick of dense hard 

 pressed boulder-clay, more gravelly and sandy than usual. Then follow 5 feet 



the back of a mass of the laminated felstone, the laminae of which are parallel to the junction-line 

 with the sandstone, but turn sharp round at an acute angle, where they abut against another green- 

 stone dyke, wliich here occupies the opposite or left side of the burn, and which cuts through the 

 sandstone from S.E. to N.W. 



VOL. XXIII. PART HI. 7 F 



