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Lower Avon as springs. Such springs, once they were started, 

 would steadily cut back till the dividing wall gave way and the 

 older river was diverted into its new course. 



After this cold came a transition to a milder period, but about 

 the actual stages of the transition we still know very little. We 

 do know, however, that the sea-level was at one time somewhere 

 about 80 feet lower than now, and then gradually rose again step 

 by step, with stationary intervals when there was time for forests 

 to grow, before they were overwhelmed and buried under marine 

 silts. During this period the valley bottoms were cut far below 

 the present sea-level, and the rivers after leaving the hill-country 

 wandered over a wide belt of flat land before reaching the sea. I 

 have not yet been able to reconstruct the topography of the 

 English Channel for the period when the lowest of the submerged 

 forests were growing ; but from evidence obtained by trawlers I 

 have been able to restore the vast alluvial plain which then 

 occupied the southern half of the North Sea. In the map in my 

 little book on Submerged Forests you will see depicted a vast delta 

 formed by the Rhine, Meuse, Elbe and other rivers. I examined 

 many dredged samples of the deposits found in the North Sea on 

 and around the Dogger Bank, and they were full of the remains 

 of freshwater and marsh plants. 



Gradually the land again sank, till the sea reached its present 

 level, probably 3,000 or 4,000 years ago. Then Bournemouth 

 must have had a prospect very much like that we now see, except 

 that the cliff was probably much lower, and a mile or two further 

 seaward. Also, Bournemouth Bay was somewhat less wide, for the 

 Needles stretched somewhat further to the west, and the 

 corresponding chalk headland of Dorset stretched further east 

 towards them. The Isle of Wight still remained for a good many 

 centuries attached to the mainland opposite Yarmouth, but this 

 attachment was only by a narrow neck, which only disappeared 

 finally in historic times. 



Thus step by step we have watched the initiation of a big 

 river system, followed by the breaking up of the catchment area 

 into a number of separate basins and valleys. Incidentally, in the 

 diversion of the Upper Avon, we have seen one of the most 

 interesting, if not the largest, instance of river-capture yet found 

 in England ; the Avon, from a small and probably peaty stream 

 becoming thus the clear and perennial salmon-river we now see. 

 Thus have originated the Valleys of Bournemouth, and their study 

 has been one of the most interesting I have come across. There 

 is, however, still much to be learnt, and you must not go away with 

 the idea that there is nothing left for local workers to do. Each 

 time we solve one geological problem others arise, which cry for 

 an answer. We still know very little of what happened in these 

 regions during the Glacial Period, or of man's first appearance on 

 the scene. 



