384 TRANSACTIONS OF SECTION C. 



FRIDAY, SEPTEMBER 1. 

 The following Papers were read : — ■ 



1: Joint Discussion with Section E on the former Connection of the Isle of 

 Wight ivith the Mainland. Opened by Clement Reid, F.R.S. 



The origin of the winding channel which separates the Isle of Wight from 

 the mainland has led to much speculation, and geographers and geologists have 

 met to-day to discuss this question. 



Unfortunately, it was only two days ago that I was asked to open the 

 debate, and I have thus been unable to refer to my notes of what early writers 

 have said as to the mode by which this winding channel was formed and the 

 island cut off. But, briefly, the early opinions were these : A hundred years 

 ago and more valleys of this sort were commonly referred to some convulsion of 

 Nature, which formed a wide rift, cutting off an island by a channel of uniform 

 width, and the width of the channel showed how much the island had been 

 shifted laterally. At the present day there is no need to discuss any such 

 hypothesis. 



Somewhat later, channels like the Solent were referred to the eroding action 

 of the sea and tide. But this hypothesis also breaks down as soon as we make 

 a careful examination of the shores of the Solent, of its tides, and of their 

 scour. The sea is neither cutting nor widening the Solent, and except in the 

 parts where the waves of the open sea can reach, there is a great tendency to 

 silt up and form wide tracts of salt-marsh or shingle. 



The third hypothesis, which is commonly accepted at the present day, is that 

 the Solent i6 a submerged river-valley which has been cut into laterally by the 

 sea and thus isolated. But opinions differ as to the direction in which this 

 river flowed. Did it come from the east or from the west? 



I am going to maintain that the ancient River Solent indubitably flowed 

 from the west, and not only so, but that at one time it was one of the largest 

 rivers in England, comparable in drainage area, and also in its relation to the 

 geological structure, with the Thames. 



If we stand on one of the hills near Portsmouth or on the central down of 

 the Isle of Wight we see at once that we are dealing with a very wide river- 

 valley. On either side of the Solent or Spithead sheets and terraces of sub- 

 angular river-gravel slope up and up to a height of at least 400 feet above the 

 sea, though in the centre of the valley they pass actually beneath the present 

 sea-level. Now these gravels have a very peculiar composition, and by tracing 

 the stones toward their source we can arrive at some very surprising conclu- 

 sions as to the direction of the flow of the ancient River Solent. Leaving out 

 of account the ice-carried erratics, which in this part of England seem never to 

 have been stranded more than 50 feet above the sea, we find that the gravels at 

 higher levels are full of greensand-chert and contain fragments of Palaeozoic 

 rocks belonging originally to the West Country. 



For a good many years the gravels puzzled me, for the old idea that the 

 cherts came from the central axis of the Weald would not account for the other 

 stones, which certainly could not have come from that district. But gradually 

 some fifteen or twenty years' work at the geological maps of Hampshire, 

 Sussex, and Dorset enabled us to trace the stones to their sources, and slowly 

 was unfolded one of the most beautiful examples of river-development and 

 river- destruction I have come across. 



The general result of this work is shown on the accompanying map, copied 

 from one published by me in the Ringwood Memoir of the Geological Survey. 

 It was not till I had worked westward into Dorset and Wiltshire that I realised 

 how important a river the ancient Solent had been. 



I will try briefly to follow the ancient river from its mouth to its source, or, 

 rather, sources, for it was a river of many heads draining an extensive area. 

 The map shows approximately its course; though minor details, when more 

 closely studied, may need modification. On the map I have attempted to re- 

 construct this river-system for a definite date. When first earth-movements 

 formed the Tertiary basins of Hampshire and London, each of these basins — 



