Yol. 50.] RAILWAY FROM ROMFOED TO TJPMXNSTER. 449 



work of this kind is seldom likely to be undertaken by a geologist 

 except as a matter of official duty. On traversing the ground 

 between Romford and Hornchurch and the Thames, I have never 

 felt surprised to find that a terrace at a given height could be traced 

 only for a few yards. Indeed, the material in which the terraces 

 are cut being London Clay, it seemed to me that nothing else could 

 be expected. For I remember, when in Cumberland, trying to map 

 some terraces on the Eden some 3 miles below Carlisle, and failing 

 to do so for more than a few yards in each case, because they were 

 cut in sandy, earthy, and clayey gravel belonging to the Glacial 

 Drift. On the other hand, 8 or 9 miles away, in the valley 

 of the Esk about Netherby, in a similar lowland, drift-covered 

 country, and on the banks of a stream of size and velocity like the 

 Eden, terraces were easily traceable throughout their course. But 

 on the Eden, below Carlisle, the harder rock underlying the Glacial 

 Drift rose perhaps 5 or 6 feet above the level of that stream, while 

 on the Esk, in the district above mentioned, it might be seen at a 

 height of more than 20 feet above the river. Similarly, on the 

 Thames terraces are frequently distinct where it flows through the 

 Chalk, as at Henley and Remenham, and especially between Cookham 

 and Maidenhead. 1 



Again, it was remarked during the discussion on my first paper 

 on this new railway that the highest river-terrace was not neces- 

 sarily the oldest. This remark is, of course, a perfectly true one, 

 and, had I said that the highest terrace was proved thereby to be 

 the oldest, would have been a useful and timely caution. But I 

 have always felt that the word proof can scarcely ever be legitimately 

 used in questions of this kind. We have to be content with a 

 decided balance of probability. I need hardly remark that there is 

 a strong general presumption that the highest terrace is the oldest, 

 and that the lower terraces may be considered as later and later in 

 date in proportion as they approximate to the level of the existing 

 stream. 



The Thames seems to me to show no signs of being an exception 

 to the rule. A. glance at the maps illustrating the geology and 

 physical geography of South Essex shows how all probability is 

 in favour of the view that the Thames, from the beginning of its 

 existence, has, in this district, been occupied in cutting its way 

 vertically from a height of more than 100 feet to its present level ; 

 while horizontally its course has been, in the main, southerly. 

 In short, the available evidence seems to me amply sufficient to 

 show that there are no grounds for regarding the Thames Valley as 

 exceptional in the mode of its formation, and every ground for 

 supposing the reverse. And I need hardly add that, where the 

 stratigraphical evidence is as clear as it is in this part of the Thames 

 Valley, it is almost impossible that it can be counterbalanced by any 

 other considerations. Were we dealing with isolated patches of 



1 A map showing the terraces between Cookharn and Maidenhead appears in 

 Mr. Whitaker's memoir 'The Geology of London and of Part of the Thames 

 Valley,' 1889, vol. i. p. 391. 



