Notes on the Pyrenees, 501 



Perdu, and in the Valine 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 Corbieres de la Barguillere, 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- 

 gard 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 

 strata 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 

 valley are almost always narrow at their origin : of which fact 



