562 D. MILNE HOME ON HIGH-WATER MARKS ON BANKS OF THE TWEED. 
above the present level of the sea be admitted, then all the rivers must 
necessarily have had their channels that much higher than now; in which case 
flood-marks must have been made on their banks at heights suited to the 
higher channels so occupied by them. 
On the other hand, it may be said, that these high-water marks prove 
rivers to have been of larger size, if these marks indicate the width of the stream 
in former times. Now, it is true, that in those parts of the river, where there 
are high water-marks on banks immediately opposite to one another, the width 
between those water-marks is greater than the width between the lines made 
by existing floods. But in examining the map of the Tweed (Plate XXXV.), 
it will be seen that there are few spots where there are high-water marks on 
banks immediately opposite to one another ; and where such occur, it must not 
be inferred that these lines are on exactly the same level, as they would be, if 
made by the river at the same time. On the contrary, they are always on 
levels which differ a few feet, indicating that they were made by the river when 
it. flowed at different levels, and of course at different periods. A river after 
having continued to press on one bank more than another, cuts for itself a 
deeper channel, and then meeting with some obstruction, it changes its course, 
and begins to press against the opposite bank. Hence, the banks will show 
flood-marks at levels not exactly the same. 
If it be alleged that the water marks, at the height of from 40 to 55 feet, on 
the banks of the Tweed were produced by floods in the existing channel, will it 
be also contended that the extensive flat, near the junction of the Tweed and 
Whitadder, which is about 66 feet above the channels of these rivers, was pro- 
duced in the same way? The great extent of this flat precludes such a sup- 
position. That flat must have been the bottom of a lake or an estuary; but if — 
so, the Rivers Tweed and Whitadder must have flowed into it, in which case 
their channels must have been at this place more than 50. feet higher than at 
present. Through that extensive flat, they have cut out for themselves the 
channels in which they now respectively flow ; and in the course of this opera~ 
tion, have left the water marks at different fevbis on their banks. 
Before concluding this paper, I must in candour admit, that the prablistl of 
these high terraces would have been more satisfactorily discussed, had the levels 
of the terraces been ascertained with more precision than I have been able to 
accomplish. That the terraces on the immediate banks of the River Tweed 
and its tributaries slope downwards with the rivers at most parts of their 
course, there can be no doubt. On the other hand, in some places, the terrace 
and base of the bounding cliff appears to be absolutely horizontal,— as between 
Wark and Coldstream ;—and the distance between these cliffs is so great as to 
suggest a lake. But to verify this view, the horizontality of the base. line of 
the cliffs would have to be ascertained with the greatest precision. © 

