Mr HiujJi Miller on River- Terracing. 301 



one level to another," and that successive elevations of 25 or 

 50 feet at a time must have sent separate and defined impetus 

 to points many miles inland, it is forgotten tliat, long before 

 reaching so far, the 25 or 50 feet will have been distributed 

 over dozens of rapids, pools, and waterfalls, adding here a 

 little and there a little to their height or depth. To take, for 

 instance, the case of the Tweed, the terraces of whicli ^Vlr 

 Milne Home has tried to explain upon this theory. At the 

 present day an elevation of the coast at Tweed mouth would, 

 to begin with, have twenty miles of windings to travel in 

 shales and sandstones of the cementstone (carboniferous) 

 series, through numerous pools and rapids up to Carham. It 

 would then enter upon the basin to which the Kelso river 

 terraces belong. At Makerston House it would traverse two 

 miles of rock and gorge in the Kelso trap, and would then 

 enter upon the series of persistent bends — not without their 

 rock exposures, which contain the terraces of Merton House 

 and Dryburgh Abbey. It would then encounter another rocky 

 " narrow " of some two miles in length ; and ere it could reach 

 the terraces at Bower on the Gala Water, 700 feet above the 

 sea, it would have travelled nearly the whole length of that 

 branch of the Tweed besides. We might here refer to the 

 twenty-two basins into which the Connecticut is divided, and 

 ask whether subsidences could be supposed to travel more 

 than 200 miles through all the varieties of arrangement which 

 they present ; but seeing that it might be maintained that a 

 single waterfall would interpose a check to this assumed 

 travelling, which it could not, practically, surmount, it seems 

 unnecessary to carry inquiry further.* 



* Let a lake-basin be supposed close to a cliffy shore, with only a few yards 

 of rocky water-course, and a 20-feet waterfall between it and the sea. The 

 water-course, like all others, will slowly deepen ; the waterfall, as usual, -will 

 tend to recede ; and the lake, by slow persistent processes, will, inch by inch, 

 be drained. What now will be the effect of a 20-feet elevation of the coast ? 

 No necessary effect at all. The waterfall need recede no quicker than before ; 

 the lake need be tapped neither more rapidly nor less evenly. The case is in 

 no way bettered, when, instead of a lake close to the sea, we have an alluvial 

 basin twenty miles from it, and twenty miles of mingled rapid, gorge, and 

 waterfall between. As a periodic impulse it may never reach the basin at all. 

 A 50-feet stride of elevation is an extreme assumption as regards Scotland. 

 Raised beaches exist at 25, 40, 50, 60, 75, and 100 feet above the present sea- 



