GEOLOGY 



surface of Chalk, all the intermediate strata having been tilted up and 

 denuded before the Pliocene were deposited : therefore the disturbance 

 had taken place before the Pliocene period. This narrows the limit 

 of time during which the great folding occurred to some part of the 

 Miocene, or perhaps of the preceding Upper Oligocene. More direct 

 evidence obtainable on the continent shows that the Miocene was one of 

 the great periods of earth movement and mountain building, and to this 

 period we may therefore safely refer most of the folding in Sussex. The 

 movement in Sussex seems to have consisted of a horizontal compression 

 of the strata from north to south, by which they were bent into a series 

 of folds having an east and west axis. Thus was formed the large anti- 

 clinal arch of the Weald and the syncline of the Hampshire basin, as 

 well as the numerous smaller ripples which will be found indicated on 

 the geological map. To the same period belong the very curious over- 

 thrust faults so well seen on the foreshore between Eastbourne and Beachy 

 Head, though these happen to run north and south for a short distance, 

 for they apparently occur just where one fold is dying out and a fresh 

 one commencing. All the folds are elongated domes, arranged en echelon, 

 not in continuous ridges ; where one fold dies out a new one commences, 

 but not exactly in the same line and not continuous with it. 



The lateral compression of the rocks just referred to necessarily 

 caused them to expand upwards, in the only direction in which they 

 were free, to form east and west ridges. The largest of these undulations 

 would now form a mountain chain over 6,000 feet in height in the 

 centre of the Weald, were it not that rivers and sea combined to plane 

 it down almost as fast as it rose. Its uprise however was sufficiently 

 rapid to determine the course of the Wealden rivers, which flowed down 

 the northward and southward slopes, diverging from the Wealden axis. 

 During subsequent periods the country around this axis, being formed of 

 rocks more easily denuded than the Chalk, has become lowered much 

 below the level of the Downs through which the rivers now flow in 

 narrow and deep valleys. A river once started tends to deepen its 

 channel, but remains nearly in the same place long after the original 

 slopes which first directed its course have been obliterated by the erosive 

 action of its tributaries. The high cliff-like escarpment of the South 

 Downs, which overlooks the Weald, is due to the erosive power of rain 

 and rivers acting on strata some of which are hard and some soft ; it is 

 not due to the waves of the sea as formerly thought. Standing on the 

 Downs and overlooking the low-lying plain it is difficult to believe that 

 we are not looking across the bed of an ancient sea, which once filled the 

 Weald. But not only are newer Tertiary marine deposits absent from 

 the Weald, but as Mr. Whitaker has pointed out, escarpments can 

 readily be distinguished from sea-cliffs by certain characteristics. The 

 foot of a sea-cliff keeps to one level, but cuts through various strata ; the 

 foot of an escarpment formed by rain and rivers rises and falls consider- 

 ably, but keeps to the same geological horizon. The northward-facing 

 slope of the South Downs is an escarpment always having at its base the 

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