MAPS AS GEOGRAPHICAL ILLUSTRATIONS 505 
Bar must have been progressively shortened as the south-flowing 
stream grew headward. While this change must have gone on 
rapidly for a time following the epoch of capture, its future 
progress must be extremely slow, because the slopes of the two 
sides of the divide at the head of the Bar are now not very unsym- 
metrical. 
This set of sheets furnishes the best example of a diminished 
stream wandering on the aggraded floor of a meandering valley 
that has come to my notice. 
THE COAST OF GASCONY. 
SINSEUS 70, UGG, MON FOP. AO, ailaly Ait is 
A great part of the smooth low plain—the Landes — of south- 
western France exhibits to a nicety the uncarved initial form of 
an almost infantile coastal plan of Pleiocene strata. Its surface, 
seldom cut by streams and marshy in many parts, may be 
traversed for miles without perceptible inequality. Roads, rail- 
ways, and property lines follow straight courses for long distances. 
Where streams occur, they occupy very narrow, steep-sided 
valleys of slight depth, leaving the broad interstream spaces 
with very imperfect drainage; once the home of the stilted shep- 
herds. 
The harborless coast line of this district, from the mouth of 
the Garonne southward to the Pyrenees, is of remarkable, indeed 
of exceptional straightness: for miles together, its departure 
from a direct line is hardly perceptible. Dunes fringe the whole 
extent of this even coast, and stretch inland over a belt of from 
two to four miles wide. Their invasion of the plain has been 
largely arrested by planting pine trees. The dune barrier effec- 
tually encloses the water from a number of the streams, which 
then collects in sub-triangular lagoons, or ééangs. One of these, 
the basin of Arcachon, is supplied by the largest stream of the 
district, and maintains an open channel to the sea; here the quiet 
étang is replaced by a mud plain that is alternately covered and 
bared with every run of the tides. It possesses the short, blunt 
water courses, characteristic of tidal scour on a debatable land 
