AND GEOLOGICAL RELATIONS OF CERTAIN HOT SPRINGS. 
597 
confident as to the correctness of the statement. Near Aldus there issues from the lime- 
stone abruptly an entire rivulet of the clearest water; temp. 46°*1 Crichton = 45 0, 5 
reduced. 
XI. Ussat, near Tarascon. 
A. Geological Position , fyc. — Of this place, too, I have little to say. It is seated on 
the bank of the Arriege in the department of that name. The valley is here com- 
posed of limestone, precipitous, and full of caverns. We should be disposed to con- 
jecture that this, as well as the neighbouring metalliferous valley of Vicdessos, owed 
its origin to a process of disruption. The granite here is also very near, though not 
exposed immediately at Ussat. It is a portion in immediate connexion with the vast 
granitic nucleus of the Eastern Pyrenees. Elevation above the sea according to 
Parrot, 1654 feet. 
B. Specialties , 8$c. of the Springs. — The mode in which the springs of Ussat rise is 
worthy of notice, though they are not well adapted for determining fixed tempera- 
tures. The waters are ferruginous ; there is no great spring, but each bath is filled 
by means of a hole bored in the sand in which it is excavated, through which the 
water rises. Each has therefore its own temperature, and the heat is not great. 
Under the circumstances I did not think it worth while to determine it, especially as 
the water flowing constantly through the bath is exposed to be cooled by the contact 
of air. 
XII. Ax*. 
A. Geological Position. — In this most remarkable thermal site, reported to be the 
most prolific in Europe, we are not disappointed in finding a complete confirmation 
of the general principle that hot springs take their rise at the boundary of granite. Ax 
is seated on the river Arriege, several leagues above Ussat. We pass from limestone 
to slate, and from slate to granite, exactly at Ax. This granite immediately rises 
into lofty mountain masses, forming a sort of nucleus or centre of elevation, com- 
prehending the sterile country between Ax and Mont Louis. It is here that in all 
the extent of the Pyrenees, reckoning from the Atlantic, the granite first constitutes 
the ridge or geographical axis of the chain, though it invariably forms (where visible) 
the geological axis. From this group of granitic mountains the country slopes in 
three directions, to the east, north, and south. It may, in fact, be viewed as the true 
termination of the ridge, which gradually descends by subdivided ramifications to 
the Mediterranean, the chain being split by the valleys of the Tet and Tech running 
east and west, which are not to be viewed as longitudinal valleys, but as valleys ra- 
diating from this the most easterly centre of elevation, just as the transverse valley 
of the Arriege radiates to the north, and that of the Segre to the south-west. It is 
important to keep this in view in examining the magnificent circuit of hot springs 
which surrounds this granitic nucleus. The system of the Canigou, though perhaps 
* In the name Ax we trace the word Aqua, as we also do in the appellation of a multitude of points cele- 
brated for hot springs in France and the Pyrenees ; as Aix, Chaudesaigues, Caldegas, Escaldas. 
