134 
Tke JFater Economy of France 
Loire in that part of its career receives no tributary on its right 
l)ank. Not so on the left, whence she receives the Cher, the Indre, 
and the Vienne. These rivers likewise spring from the crys- 
talline formation, but some fall into beds hewn out of the lower 
chalk, between hills having at their summits some remants of 
tertiary deposits. From Angers to the ocean the bed of the 
river becomes narrowed between higher banks, and the geolo- 
gical strata over which it flows belong to the older formations, 
such as the Devonian and the Silurian. The mean flow of the 
Loire, as ascertained by M. Daue is as follows : — 
At St. Just and Andressieux, not far from its source, it gauges 
1320 gallons per second ; at Roanne, lower down, where it begins 
to be navigable, 1540 gallons per second ; at Briare and Orleans, 
(3600. At the time of its great freshets, the quantity of water 
that flows at Roanne reaches sometimes the enormous amount of 
880,000 gallons per second ; at Ancenis, between Angers and 
xNantes, 2,000,000. 
The two great rivers that form the Gironde, at their junction 
at Bee d'Ambre, near Bordeaux, viz., the Dordogne and the 
Garonne, greatly differ as to their origin and the geological strata 
which they traverse in their course. The Dordogne takes its rise 
in the great central mountains of Cevennes, out of the igneous 
rocks of which they consist ; then passes through Jurassic strata ; 
and, lastly, over tertiary deposits down to the ocean. On the 
other hand, the Garonne, in a course of 550 miles, waters no 
less than nine important departments of the south -of France ; 
and from the richness of these districts and the fame of their 
produce, derives an importance second to that of none of the 
other great French rivers. As already stated, it springs from 
the granitic peaks of the eastern Pyrenees ; but most of its left- 
bank tributaries issue forth from the chalk buttresses of the more 
western Pyrenees, and flow over secondary and tertiary strata. 
The Garonne gives at Toulouse an average of 26,400 gallons of 
water per second. In times of freshets it rises up to 24 feet 
above the mean height, and gives 1,320,000 gallons of water per 
second. Its waters contain a strong proportion of silicic acid, 
and a noticeable quantity of other mineral salts. 
That part of the Rhone basin which belongs to France, to- 
gether with that of the Saone, comprises an area of nearly 
28,000,000 acres. The source of the Rhone is among the crys- 
talline rocks of the St. Gothard. On its way through the canton 
of Valais it flows over the calcareous and schistose rocks which 
characterise the Jurassic formation of the Alps ; it then falls 
into the Lake of Geneva, where it rests awhile ; from Geneva 
to Lyons its bed partakes more or less of the character of the 
hills that confine it ; from Lyons to Valence it flows under 
