THE SUB-OCEANIC DEPRESSION, ETC. 427 
the most western of the southern affluents of the Garonne 
and the most eastern of the southern affluents of the Adour 
having no greater elevation than the land between two 
affluents of either of these rivers. And between the main 
rivers themselves where they approach each other, between 
a few miles from Agen on the Garonne and Aire on the 
Adour, there is only a maximum elevation of 300 feet 
above the level of the sea. So that the entire area between 
‘the River Garonne and the Pyrenees may be considered to 
be physically but one hydrographical area, that with a 
greater volume of water, a greater fall, and consequently a 
much greater momentum of water-flow, would be drained by 
one river-system, since such conditions are calculated to give 
a straighter flow and a more direct discharge of drainage. 
It is therefore highly probable that before the surface 
reached its present low level, and while the volume and 
momentum of the river-water was much greater than at 
present, the drainage of the whole of the great area between 
the Garonne and the Pyrenees, and now flowing in two 
river-systems, would be discharged into the sea from one 
river-mouth. This mouth, there is reason to think, was at 
the part of the coast where is now the deep water near 
the head of the Fosse de Cap Breton which bears the name 
of “ Le Goul,” and is opposite to Cap Breton. 
A straight line joining Le Goul with the nearest point on 
the River Garonne, where it bends from a westerly to a 
northerly direction, near Port St. Marie, passes close to the 
River Adour at the point of the great bend in its direction 
from the north-west to the south-west between St. Sever 
and Dax and about ten miles from the latter town. This 
line is, moreover, nearly coincident with the valley of the 
chief northern affluent of the Adour, the River Midouze, for 
many miles. 
And, indeed, even in recent times, and after continued 
subsidence had lowered the whole area to its present levels, 
it is known that the Adour entered the sea at Cap Breton, 
and then subsequeutly the mouth of this river was at a point 
on the coast still farther north that yet bears the name 
Vieux Boucan. Vieux Boucan is about twenty-five miles 
north of the present mouth, to which the river was finally 
diverted in the year 1579, and which outlet has to be main- 
tained for the benefit of the city of Bayonne by costly 
engineering works. Thus the River Adour itself has had 
three different positions for its embouchure. 
