TERRACES AND RIVEK VALLEYS OP WESTERN EUROPE. 281 



minor canons of Western America, with the addition of 

 a mountain range, probably snow- clad from foot to summit, 

 in the background, and a great ocean stretching away in- 

 definitely along the front. No scenery at all comparable, 

 except perhaps in western Norway, is now to be found in 

 the European area. 



Were there no other sub-oceanic channels throughout the 

 whole region here under review than that of the Adour it 

 would of itself be sufficient to demonstrate its own fluviatile 

 origin and that of all the others here described. For what 

 are the characteristics of a river-valley draining a plateau 

 and adjoining regions? They are: first, a continuous 

 deepening of the bed of the channel in the direction of the 

 outlet; second, continuous widening of the channel in the 

 same direction ; third, a winding course ; fourth, lateral 

 tributaries descending on one or other of the sides to join 

 the main stream. AH these characterise the sub-oceanic 

 channel of the Adour. On the other hand, they are not 

 characteristic of seismic fissures, or of fissures formed by 

 faidts or any other process with which Ave are acquainted on 

 the land surface. We are familiar with valleys with similar 

 characteristics, but waterless, entering the great valley of 

 the Nile or the shores of the Red Sea, or traversing the 

 region of Arabia Petrsea and Southern Palestine, where 

 rainfall is either absent or only intermittent ; but we do not 

 hesitate to recognise in them the channels of former streams 

 and rivers, though they are now dry; and not less certain is 

 the nature of these sub-oceanic channels now covered by the 

 waters of the Atlantic, such as those of the Loire, Adour, 

 Douro, and Tagus. No other theory than that here advanced 

 will, I venture to hold, serve to explain their origin and 

 presence under the waters of the ocean. 



VI. The Submerged River-Channels off the Coast of 

 Spain and Portugal. — The western submerged escarpment 

 off the shore of Spain and Portugal is characterised by 

 several remarkable river-channels and caiions, of which the 

 most important are those of the rivers Caneira, Arosa, Lima, 

 Douro, Mondego, and the Tagus ; besides these there is a 

 grand canon to the north and west of Cape Carvorino (lat. 

 39° 30' N.) which may have been the combined channel of two 

 or three now unimportant streams; we shall consider these in 

 their order of succession from north to south. (Plate IL) 



(a.) The Caneira.— A short, but well defined canon indents 

 the Great Declivity in long. 5° 40' W. opposite Cape Penas. 



