550 D. MILNE HOME ON HIGH-WATER MARKS ON THE 
forms the boundary between England and Scotland in the west, running for 30 
miles in an east and west direction, follows the line of a great fault. He 
ascribes to the existence of similar dislocations, the course taken by a number 
of other rivers in the west of England. (Lond. Geol. Journal” for 1872, 
p. 156). 
The Tweed is no exception to the rule. There are three whinstone dykes to 
the south and one to the north of the river, each running nearly east and west. 
In examining the strata on the banks and in the channel of the Tweed, 
there are many proofs of disturbance, as at Tweedmouth, Horncliff, Norham, 
Coldstream, and Carham. 
The mining operations of the Berwick coal field, extending along the south 
bank of the river for about 20 miles, show down-casts amounting to as much 
as 500 feet. Between Norham and Horncliff, in the bed of the river, there 
may be seen a great down-cast of the red sandstone rocks. The vacuity thus 
formed, is now occupied by enormous deposits of sand and gravel. 
On this subject, a book has lately been published by Mr Kinaunan of the 
Trish Geological Survey, entituled “Valleys and their Relation to Fissures, 
Fractures, and Faults.” Mr Kinawan shows that most of the Irish rivers 
run along lines of rock dislocations ; and oddly enough, these fractures of the 
earth’s crust run in Ireland as in Scotland, east and west. 
On these grounds, I think it was a true remark of Sir CHARLES LYELL, in his 
“ Principles of Geology” (vol. i. p. 335): “ Few great valleys in any part of the 
world have been excavated by rain and running water alone. During some 
part of their formation, subterranean movements have lent their aid, in accelerat- 
ing the process of erosion.” 
2. If then, the River Tweed now runs along lines of great fractures of the 
strata, the question suggests itself, What has become of the millions of frag- 
ments from the dislocated rocks, many of these fragments hundreds, perhaps 
thousands, of tons in weight ? 
The river now runs over a level channel which externally manifests no rents 
or fractures ; nor is there any external vestige of them in adjoining districts. 
Yet when these fractures occurred, there must have been many vertical cliffs 
of strata, several hundred feet in height; all of which have disappeared. 
The lines of fracture are entirely concealed under extensive drift deposits; 
and even when these deposits are artificially removed, so as to expose the 
rocks beneath, the rocks are found in most cases forming a tolerably even 
floor, levelled, no doubt, by agents which passed over them and planed them 
down. 
I am aware that the prevailing disposition of geologists, is to explain almost 
everything by the action of glaciers and land ice; and I admit, that there 
are places in the Scottish Highlands, where that explanation is sound. 


