Notes on the Pyrenees. 501 
Perdu, and in the Vallée d’Aure. The lateral chains formed 
by the transition rocks have marked peculiarities, and an in- 
dependence as chains, as strongly marked by their physical 
characters as by their geognostic constitution: such are the 
chains of the Corbiéres de la Barguillére, Mont de Pinet, &c. 
The primitive crystalline rocks form several extensive lateral 
chains; those in the east are continued by the Pic de St. Bar- 
thelemy to the valley of Saleat, presenting in their course 
cols, or ports, as in the principal chain. The direction of the 
granite mountain of Irsovia Mendi, or the line of its greatest 
extent, is nearly parallel to that of the chain. It results from 
the relation of transverse and lateral chains, that chains which 
are transverse to the principal have others perpendicular to 
themselves, and generally similar in structure, which may be 
parallel to the principal chain, the latter generally giving rise 
to one rivulet or more; and the relation of the lateral to the 
transverse chains must be the same as that of the former to 
the principal, the transverse being mostly of a similar struc- 
ture. It also results from this disposition, that the generality 
of the Pyrenean valleys, originating from the crest of the prin- 
cipal chain, are transverse with respect to it, but longitudinal 
with respect to the transverse chains, which also originate 
from the main crest; while the valleys dividing the moun- 
tains, and forming the line of the crest of the perpendicular 
chains, transverse with respect to them, are parallel with re- 
ard to the main chain, and to the valleys dividing the lateral 
or parallel chains. Most of the transverse valleys of the Py- 
renees, as previously remarked by Ramond and Charpentier, 
present at their origin a vast basin, in the form of an amphi- 
theatre, or a succession of basins, which rise one above the 
other ; so that the valley, instead of offering a uniform slope, 
rises by so many stages towards the crest of the chain. This 
arrangement occasions the mountain torrents descending 
from above to form cataracts or falls; but this, as in fact the 
diminution in size or contraction of these basins or oules 
(alles): as they are termed in the language of the country, we 
have always observed to be connected with other geognostic 
changes. 
The valleys which divide the parallel chains are alone truly 
longitudinal. They occur generally in the direction of the 
str a of the mountain ; and the difference between the direc- 
tion of the valley and that of the strata affects the formation 
of caverns. Charpentier has remarked, in the Pyrenees, that 
the entry of valleys terminating in the plain is sometimes 
large, sometimes narrow; but valleys terminating in another 
. . . f—) . 
valley are almost always narrow at their origin: of which fact 
