IN THE SOUTH OF ARE AX, 531 



burn to the south. It is very hkely one of the beds of stones which Ave saw in 

 the last section. There are also other indications of water-sorting in the beds 

 l)oth above and below. Shells were most abundant near the rock, and also higli 

 up the bank to the south end of the section. 



Above this a great mass, 30 to 40 feet high, of laminated felstone, in a 

 very shattered and rotten state, crosses the valley. The channel cut through 

 this is only the breadth of the burn, and in this narrow passage are a few old 

 rounded, but not striated surfaces ; but elsewhere I could see none, so completely 

 is the whole rock in a splintery state. The boulder-clay lies over the top of this 

 rock, and comes down to the burn both above and below it. I unfortunately 

 neglected to measure the height to which this rock barrier rises above the burn, — 

 a point so far of importance that the rock, if it really cross the valley, as it seems, 

 must have formed a dam behind which the glacier ice, coming down from the 

 hills above, would be checked and embayed in the basin above. Of course it 

 may have accumulated till it rose high enough to overflow the barrier, but tlie 

 narrowness of the passage, obviously cut by water, indicates plainly that through 

 it the ice found no egress. 



Above this barrier is an open basin half a mile long (Plate XXL fig. 6*.), 

 round which the boulder-clay lies deep. The curve of the bank all round faintly 

 suggests a water-formed terrace, but I did not attempt to ascertain how far it keeps 

 the same level. The lower end of the basin is about 300 feet above the sea, the 

 upper about 380. It was in the boulder-clay bank, about 20 feet up from the burn 

 at the lower end of this basin, that I found the last fragment of shell I met with, 



Plate XXI. fig. 1, gives this bank. The lower part of the bank consists of 

 a singularly hard, dense, dry, gravelly clay, derived from felstone porphyry rather 

 than from the sandstones. It looks as if it had been jammed in dry against the 

 felstone rock, to the east and south down the burn, by the glacier when in 

 motion. In it are several large, well striated greenstone boulders. Above this 

 hard gravelly clay, to the left, the red boulder-clay rises to the top of the bank. 

 To the right this boulder-clay has been stripped off, and over the surface of the 

 underlying bed is a stratum 2 or 3 feet thick of water-rolled boulders. This 

 bed merely laps up on the edge of the red boulder-clay as it thins out on the flat. 

 The relation of the two is indeed very difficult to make out from the debris and 

 turf which conceal their junction in the corner at the rise of the bank; but it is 

 better seen at the other end of the section of their junction-line, where it is ex- 

 posed about 100 yards up the burn, and this is shown in Plate XXII. fig. 8. Here, 

 as before, the hard yellow gravelly clay, about 6 feet thick, lies in the burn 

 course, and, resting directly on it, is the bank of red boulder-clay. To the left, cut 

 off by the burn, is seen the projecting edge of the valley flat. Here the yellow clay 

 seems to have been eroded and buried under a thicker mass of rolled stones and 

 gravel, which becomes thinner as it is followed down the edge of the bank to the 



VOL. XXIII. PART III. 7 E 



