
BANKS OF THE TWEED AND SOME OF ITS TRIBUTARIES. 559 
The bearing of these facts on the river terraces will at once be seen. 
If the sea stood, as suggested in the early part of this paper, at 180 feet 
above its present level, the Rivers Tweed and Teviot must have reached what 
was then the sea, at points respectively some miles to the west of Kelso. 
When the sea sank to the level of 120 feet, the junction of the above rivers 
with the sea, would be close to where Kelso is situated. 
When another subsidence of the sea took place, say to the level of 60 or 
70 feet, afterwards to 30 or 40 feet, and ultimately to 12 or 15, the rivers, 
being on each occasion made to flow down steeper gradients, would acquire 
greater speed and more cutting power. Their channels being deepened, their 
banks would also be undermined, and any flood marks previously made on 
their banks, in the upper parts of their course, would run great risk of being 
obliterated. 
There is thus a relationship between the old sea margins and the high river 
terraces. As the sea fell from one level to another, so also must the rivers 
have fallen from one channel to another. 
There is, however, this difference between the two. If the successive 
subsidences of the sea were sudden, the subsidence of the rivers could not 
have been equally sudden, as time would be required before their streams could 
cut out deeper channels. How much deeper the new river channel would be 
than the old, would depend on many circumstances. It would not be equal in 
every river. It would not be equal even in every part of the same river. 
Therefore the old flood marks on river banks, after the rivers sank in conse- 
quence of a subsidence of the sea, might not be all at an equal height above 
the deeper channel when acquired. But still, there would be im all rivers, 
traces of an old flood line above that of the existing stream, when the materials 
composing the bank were such as to have been susceptible of erosion, and when 
the banks were not so undermined as to destroy the old flood lines. 
The examination of these high river terraces has obtained attention from 
only a few geologists. The cases of which I have found notices, may be 
mentioned. 
Our esteemed colleague Mr Brown, in his paper to which reference has 
already been made, vouches from personal observation, for the existence of 
three distinct terraces on two rivers in Perthshire with their tributaries, viz., 
the Earn and the Teith. 
On both rivers, he states that there are three terraces. In the Earn, these 
are at 9 feet, 22 feet, and 57 feet above the present channel of the river. 
On the Turrit and Ruchil, tributaries of the Earn, the same three-fold system of 
terraces exists. 
On the River Teith, though the same terrace system prevails, and if possible, 
more strikingly (p. 154); and also on the Keltie, a tributary of the Teith, the 
