6C2 DENUDATION AND SCENERY, 



low-lying districts formed of Glacial Drift. On the borders of 

 Norfolk and Suffolk, the Little Ouse and the Waveney appear 

 to rise in a marshy tract at Lopham Ford ; this feature may perhaps 

 have originated from the parting of one stream or from the wasting 

 back of the Boulder Clay that formerly separated two drainage 

 areas. Streams must often find a water-parting underground, and 

 to their divergence in this way may be attributed the formation of 

 outliers, which are patches of a formation that have been separated 

 from the main mass or escarpment by denudation. We may see 

 them in various stages of formation in the spurs of the Oolitic 

 ranges, and the isolated knolls or outliers probably owe their 

 preservation to slight undulations in the strata, which have in- 

 fluenced the direction of the springs in their underground courses. 

 Brent Knoll and Glastonbury Tor are remarkable examples, and 

 they both exhibit evidence of gentle synclinal structure. (See Fig. 

 39, p. 250.) 



Where a formation is shown over an area surrounded by newer 

 strata, the exposure is termed an Inlier, and this is usually initiated 

 by disturbance or irregular undulations, as in some of the 'Valleys 

 of Elevation ' previously mentioned. In other instances we find 

 masses of older rocks encircled by newer formations, standing out 

 like islands, as in the hills of Carboniferous Limestone near Wells 

 in Somerset that rise through the New Red Rocks and Lias. Here 

 we see the scenery of older periods revealed by denudation in 

 more recent times. 



It will be easily understood why the Alluvium should form such 

 scenery as it does — belts of low-lying meadow land bordering the 

 rivers and streams. It must be remembered, however, that changes 

 of level greatly affect denudation and deposition. A slight sub- 

 mergence would cause a river to flood its banks and deposit 

 sediment, whereas elevation would tend to make it deepen its 

 channel and so remove more material. A river, as is well known, 

 is incessantly changing its course in however small a degree, and 

 when we see broad flats of Alluvium bordering a small stream, 

 it does not follow that the stream ever entirely filled that wide 

 channel, but that in the course of time it has occupied different 

 positions in it. (See pp. 513, 521.) The nature of the river valleys 

 of course depends upon the character of the rocks traversed by the 

 stream, bold cliffs being commonly formed in hard rocks, but hardly 

 ever in soft strata. Hence, we often find rivers apparently doing 

 little towards the excavation of their valleys, and in fact only 

 shifting material they have previously accumulated. This may 

 be due to the depression or low elevation of the tract, or to a 

 diminished rainfall, and in part to alterations in the surface strata 

 from denudation, whereby larger areas of porous rocks are laid 

 bare at the surface, so that much of the rainfall is carried away 

 underground. (See also Fig. i, p. i.) 



The Broads (so named from the Anglo-Saxon Bra-dan ' to 

 broaden') form a distinct feature in East Norfolk. They are 

 expanses of freshwater that occupy the lower reaches of the river- 

 valleys, sometimes in the direct course of the streams, but more 



