TERRACES AND RIVER VALLEYS OF WESTERN EUROPE. 283 



(e.) llie Mondego. — (Plate III.) At a distance of about 

 35 miles from the coast of Portugal at Palleiros de ]\Iira 

 (lat. 40° '6{y N., long. 9"^ 25' W.) there occurs a short, narrow, 

 but remarkably deep, cailon, cutting for a few miles into the 

 Continental Platform and bounded on either side by precipices 

 of rock froni 6,000 to 7,000 feet in height as if seen from the 

 base. The bottom of this caiion, indicated by the sounding, 

 "1170 " fathoms, is only about 8 miles from its apex : so that 

 the fall must have been at the rate of 752 feet per mile, sug- 

 gesting a series of grand waterfalls, or cascades, rivalling some 

 of the finest now in existence. This caiion is presumably that 

 of the river Mondego, towards the mouth of which it appears 

 to point; but owing to the insufficiency of the soundings 

 over the platform at this place the connection cannot be 

 established. It is possible, however, that this canon may 

 have also received the waters of the river Vouga which 

 enters the ocean at Barva Nova and has numerous tribu- 

 taries. Over the area of the platform, there may have been 

 a junctif)n of this stream with the Mondego, the channel of 

 which is now silted up. and thus the inchcation of a vast 

 mass of water foriuerly descending through the canon, which 

 its profundity suggests, may be explained. 



( /'.) Canon off Cape Carvoeiro. — A profound and well- 

 defined canon indents the Great Declivity off the coast ot 

 Portugal near (^ape Carvoeiro, in lat. 3i)° 30' N., but which 

 is remarkable for the fact that it does not appear to be 

 directly connected with any important river now descending 

 from the adjoining lands. The apex of the caiion is about 

 10 miles from the coast at Point Nazareth ; and several 

 minor streams, of which the largest is the Vieira, probably 

 united over the surface of the platform to form a sufficient 

 body of water to erode the channel we are now considering. 

 From its apex at the lOO-hithom line to its embouchure at a 

 depth of 1,500 fathoms, the length of the canon is 25 miles, 

 and along its southern margin it was hemmed in by precipices 

 of rock several thousand feet in total depth. The most 

 precipitous part is just to the north of Burling Island Avliere 

 there is a nearly sheer descent of about 5,000 feet. In Plate 

 111, I have drawn sections across this cafion at three 

 successive intervals from the higher to the lower levels. 



(_(/.) The Grand Canon of the Tagus. — (Plates II and III.) 

 No doubt can be thrown on the identity of the submerged 

 channel of the chief river of the Peninsula as its apex is 

 directly in front of the mouth of this river at a distance of only 



