590 
PROFESSOR FORBES ON THE TEMPERATURES 
can hardly be a doubt, though its direction is not perpendicular to that of the strata^ 
The same rocks are continued through the mass of the Pic de Bergons, on the same 
side of the ravine with Rioumaou; and I believe that the thinly slaty limestone which 
forms the summit of that hill (4501 feet above Luz by my observations, and there- 
fore 691 6 above the sea, differing only 14 feet from the measurement of Ramond,) be- 
longs to the same bed as the one above described. On the side of the Gave opposite 
to Rioumaou, or above St. Sauveur, we find a confirmation of these views. The 
alteration of the slates and limestones seems manifestly due to certain interfering 
veins of excessively hard porphyry, having a basis containing much quartz, in which 
crystals of garnet are imbedded. I conceive that these veins are connected with the 
neighbouring granitic masses. They are best seen by skirting the cliffs which bound 
the west side of the Gave, — a walk which presents both magnificent and savage 
scenery *. On the whole, I conclude that the hot springs of Bareges, St. Sauveur, 
and Cauteretz, which are placed nearly in one straight line, owe their origin in a 
great measure to circumstances connected with the presence of what modern geolo- 
gists might justly term ce metamorpliic rocks 'f'”; that these rocks are intimately con- 
nected with the granite in their vicinity ; and that distinct convulsions have accom- 
panied or succeeded their elevation. 
B. Specialties of the Springs . — The springs of St. Sauveur present but little oppor- 
tunity for increasing our precise knowledge of temperature. The four springs which 
take their rise in the town of St. Sauveur discharge themselves into one common 
reservoir beneath the street, whence the water is distributed to the baths. There is, 
however, one spring to which attention has recently been directed, which rises some 
hundred yards from the town, and a little higher. In order to arrive at its source, 
and to separate it from the cold water which accompanied it, a considerable cavern 
has been excavated. It is called La Hontalade. It is accessible within this cavern 
at a distance of ten or twelve feet from the point which is viewed as the source ; but 
as this space is passed over under the floor of the excavation, and as the cavern must 
always have nearly the mean temperature of the soil, little error is to be apprehended 
from this circumstance, provided that matters are allowed to remain as they now 
stand. 
C. Temperatures of the Springs . — Elevation of St. Sauveur 2526 feet (La Roche). 
There are many fine cold springs near St. Sauveur. One in the town had a tempera- 
ture of 54 o, 0 Crichton = 53 0- 3 reduced (this was near the hot springs) ; two others 
a little higher were 50°‘2 Crichton and 50 o, 3 Crichton, which give 49 0, 5 and 49°‘6 
when reduced. We have stated that there are reservoirs belonging to the thermal 
establishment of St. Sauveur. The consequence is, that the temperature perpetually 
varies. I have repeatedly tried it at the “Buvette.” Thus on the 20th of July 1835 
* A series of specimens illustrative of the altered slate formation, and of most of the sites described in this 
paper, has been presented to the University of Edinburgh. 
t See Lyell’s Geology, vol. iii. p. 374. 
