100 



PROF. T. M'KENNY HUGHES ON THE 



have yielded palaeolithic remains. As the river is cutting back 

 the steep ground, terraces are soon destroyed, and the rain 

 and agents of degradation keep handing down to lower levels 

 all superficial deposits as soon as formed — so along such valleys 

 great masses of rainwash, or head, or run of the hill gather in 

 hollow places or on ledges ; all surface soils merge into such 

 accumulations. Where the ground is covered by vegetation it is 

 to some extent protected; but where the sod is broken, the rain soon 

 undermines and sweeps out the soil, and a ravine is formed. A 

 hole scraped for shelter by a sheep may let the water through the 

 turf and start the work. Looking out on the east from the train 

 near Lowgill Junction in Westmorland, about an acre of land may 

 be seen covered with stones to about 10 feet deep in places. That 

 was all done in about two hours in a thunder-storm, and the gashes 

 from which this debris was swept out are seen on the fellside 

 above. At the mouth of each little gorge along the Upper Ehone 

 a fan-shaped mass of torrent- debris is protruded into the valley. 

 These look like the fragments of moraines as you drive down the 

 valley over a succession of hills, now hanging on to this side, now to 

 that side of the valley. A more careful examination, however, 

 especially from higher ground, soon shows their real character. So 

 in the smaller valley of the Clwyd there are masses of torrent-debris 

 of postglacial age protruded into the vale, as, for example, out of 

 the gorge by Denbigh, from the valley of the Clwyedog, or from the 

 smaller tributary streams. But all the while along the slopes the 

 rain brought down the soil and stones, leaving the rocks bare here 

 and there to be disintegrated and furnish more material. 



Such debris, derived almost exclusively from Silurian rock, was 

 pointed out to us by Mr. Strahan in a road- section east of Tremeir- 

 chion. Where there is soft drift the rainwash is, of course, different, 

 and is more readily transported ; but sooner or later every loose 

 material travels down the hill. Where the soil is bared by plough- 

 ing, the downward waste is often very rapid. In every long-culti- 

 vated hill-country there are terraces so formed. Each man turns 

 down the soil from the upper side, so it accumulates at the lower 

 end of his allotment, and is removed from the bottom of the bank 

 that separates him from his neighbour on the slope above (see fig. 5, 

 p. 111). Thus, in a manner accidentally, are formed the terraces 

 known as " raines " in the north of England. 



There are many tests to apply when we are trying to distinguish 

 between a marine shingle, a river-gravel, and the rainwash or run- 

 of-the-hill. 



A marine shingle has the finer and coarser gravel somewhat 

 sorted, but the up incline and the over-bank tip are quite distinct. 

 Even in the case of shingle thrown against a cliff there is often 

 a ridge of thrown-up gravel a little way from the rock ; this is 

 caused by the recoil of the wave. Just as we may often notice 

 along the pavement on a gusty day, the dust is laid, not along 

 the base of the wall, but in a ridge nearer the middle of the pave- 

 ment, being driven off the wall by the rebound of the wind from 



