584 
PROFESSOR FORBES ON THE TEMPERATURES 
I. Eaux Chaudes. 
A. Geological Position. — The locality of these springs is one of the most interesting 
in the Pyrenees ; and though there are few parts of the whole chain which excel it in 
romantic beauty, it is little known or visited. The Vallee d’Ossau, which conducts 
the traveller almost due south from the town of Pan, stops abruptly at the town of 
Laruns, or rather divides into two parts, of which the more conspicuous turns to the 
eastward, forming the valley of the Eaux Bonnes; whilst the other consists of a mere 
chasm, at its entrance narrow and tortuous, but increasing in sublimity as we ascend, 
which furnishes the chief tributary of the Gave* d’Oleron, and which descends di- 
rectly from the Pic du Midi d’Ossau. The rock here is a limestone, probably transi- 
tion, but which rests immediately upon the granite. The limestone for the most part 
rises towards the granite, and ultimately rests upon it, as if vertically elevated by it. 
The hot springs occur exactly where the limestone meets the granite, near the bed of 
the river; those whose source I was able accurately to trace, issue from granite, 
which is here a beautiful rock with greenish felspar. This valley is more obviously 
one of disruption than almost any other I could name ; it resembles the pass of the Via 
Mala near Splugen in the Alps. It rather increases in breadth above the baths, but 
with mural precipices on both sides of very great height. The direction of the fissure 
or valley is nearly parallel to the line of dip of the limestone strata^-. 
B. Specialties of the Springs. — The springs of the Eaux Chaudes are numerous and 
of very various temperatures. Most of them, however, are conveyed in pipes from 
stone reservoirs at a considerable distance from the baths ; and as I had no means 
of examining these but where they flowed into the bath, the determinations of these 
temperatures have but little interest (comparatively). Wherever we have either 
cisterns, by which the water is intercepted before it can be examined, or long con- 
duits, it is clear that the temperature may be affected by that of the air or of the 
ground, and is therefore variable with the season and other circumstances. To this 
class belong the Esquirette, Clot, and Rey, which therefore are marked with an 
asterisk, having been taken at the bath cocks. The Arreseeq and Baudot were taken 
where they issue from the granite, being merely conducted by short tubes through 
small vertical walls built so as to sustain the rock from which they issue. They are 
in the open air. The springs are all sulphureous. 
* It is hardly necessary to observe that Gave is the provincial name for a mountain stream in the Pyrenees. 
t See Mr. Hopkins on Physical Geology, Cambridge Transactions, vol. vi. 
