River-Valleys off the Coast of Portugal 
passage, producing a cafion of limited length, but in“its features grand in the extreme ; only represented, 
perhaps, by some of the fjords of Norway at their upper sources. The river descending this ravine must 
have given rise to a series of lofty cascades or waterfalls, rivalling some of the finest of the present day. 
This cafion may have received the waters of the Vouga, which enters the ocean at Barra Nova and has 
numerous tributaries. But presumably the silting up has effaced from the chart the connecting channel. 
Caiion off Cape Carvoeiro.—A profound and well-defined cafion indents the Great Declivity off the 
coast of Portugal, N. of Cape Carvoeiro in lat. 39° 30’ N., and is remarkable for the fact that it does not 
appear to be directly connected with any important river now descending from the adjoining lands. 
From its apex at the 100-fathom contour to its embouchure at a depth of 1500 fathoms (go000 feet) its 
length is about 25 miles. Its southern side is nearly a straight line, and is a precipice of several thousand 
feet in its deepest part—suggesting a line of fault or fracture. Its most precipitous part is immediately 
to the north of Burling Island, where there occurs a sheer descent of about 5000 feet ; and its apex is 
8 miles from the coast! The unique character of this cafion, so well defined and remarkable for its 
features, leaves us in complete ignorance regarding its origin and mode of formation. 
The Grand Caiion of the Tagus.—In the case of this, the chief river of Portugal, the abmenee 
channel is almost continuous with that of the river itself when it emerges from the lake which 
constitutes the magnificent harbour of Lisbon, 11 miles in length and 7 broad, with a narrow channel 
(Entrada do Tejo) down which the current flows very swiftly into the ocean, There can be no doubt 
regarding the identity of the submefged channel with that of the river itself on issuing from the lake, as 
its apex is directly opposite the latter at a distance of only 5 or 6 miles, immediately south of Cape 
Razo. The small quantity of silt by which the channel is encumbered, as compared with the other 
streams above described, is due to two circumstances: first, because the mud of the river above the 
lake is precipitated over the floor of the lake itself; and secondly, because of the strong current above 
described, by which the clear waters are discharged into the ocean through the channel. 
Like several of the submerged valleys already described, that of the Tagus is characterised by a 
double outlet, forming in plana Delta. After descending from its apex for a distance of 35 miles in a 
westerly direction, and to a depth of 600 fathoms, the channel divides: one branch, which is the deeper, 
continuing very much in the same direction ; the other sweeping round in a semicircle to the north- 
west, and ultimately entering the deep ocean at a distance of about 15 miles from the mouth of the 
former and deeper channel. There is thus enclosed a large tract, the highest part of which rises to 
within 66 fathoms of the present surface of the ocean. ‘Towards the embouchures of these rivers, the 
waters must have entered the ocean in a series of cascades, with a total descent of over 5000 feet within a 
distance of 6 or 7 miles.? 
During this period of great land elevation, the uplands and mountains of Portugal were covered by 
snow and glaciers, which have left their remains and effects very clearly over the surface of the land at the 
present day, in the form of ice-worn rocks, roches moutonnées, and moraines—vividly described by Sgr. 
J. F. Delgardo,’—and which must have sent down vast floods of water through the Tagus, especially 
ey 
during the “période pluvieuse et tempérée”” which characterised the Interglacial Epoch, both in Portugal 
and in the British Isles. ‘The phenomena which characterise the past and present conditions of this great 
river are of much interest, and are well worthy of investigation by students of geography. With 
this digression we conclude our observations of the submerged river-valleys of the Peninsula. 
1 In the series of sections crossing this cafion,in Zrans. Vict. Inst. vol. xxxi. p. 283, at three successive stages, I have endeavoured to represent 
its increasing depth from east to west by scale. See Plate VI. 
2 The soundings indicate a descent of 600 to 1200 or 1300 fathoms (7200 or 7800 feet). 
3 Note sur Dexistence d’anciens glaciers dans la vallée du Mondego (Lisbon, 1895). 
