Geographical Collections. 209 



wims of the positive ordinates are equal to the sums of the negative ordinates. 

 There are other phenomena attached to the geography of mountain chains of 

 more or less importance, and among these their aspect and outline form interest- 

 ing features. One of the first phenomena which strike the eye of the observer 

 on approaching a mountain chain, is the line of demarcation with the plains below. 

 Thus the Pyrenees are bordered on the north by a plain which permits of their 

 being seen at a great distance ; while, on the southern aspect, transverse chains, 

 succeeded by isolated masses, advance far into the kingdom of Spain. The 

 plains of Lombardy stretch to the very foot of the Alps, forming a well marked 

 line at the foot of the hills. The same occurs in the plains of Tartary ; which, 

 according to Cordier, probably attain an elevation of 3000 metres above the level 

 of the sea — a calculation much exceeded by Barrow. The extent of the base is 

 found to vary in different formations ; but, as a general fact, mountains which do 

 not form a part of a chain, or that are more or less isolated, have the most ex- 

 tended base. Almost all the accidents presented in the phenomena of the moun- 

 tain chain of the Pyrenees, whether in their grouping, their alignation, their de- 

 partition,* their approximation, the regularity of their acclivity, the uniformity of 

 their height, the form of their summits, or in the general accidents which ac 

 company them, are attached to similar circumstances. Leaving the extensive 

 Landes to the north-west, the chain is approached, after crossing the Adour, 

 through a country of hills of alpine limestone ; their height is insignificant ; 

 their summits rounded ; and their acclivities or their valleys clothed with luxuriant 

 crops, or the scattered huts of the Basques. The granitic mountain of Irsovia Mendi 

 presents itself at the foot of the Pyrenees ; but its summit is rounded. Several 

 hills of old red sandstone are traversed near St. Jean pied de Port, without any 

 difference in outline being perceptible. From the latter town there is a great 

 road to Mauleon, which recedes northward round long transverse ridges of tran- 

 sition rocks, from whose rugged heights are just perceptible the snow-topped 

 mountains and secondary rocks which constitute the principal crest in this part 

 of the chain. The green sward, crowning the outlying hills, effects a gradation 

 with the plains below ; the dark tint of the bare rocks on the acclivities, dimi- 

 nishes the intensity of the shades ; while the eternal snows lose their lofty sum- 

 mits in the passing clouds. 



The disposition generally assumed by the alpine limestone is that of gentle slopes 

 in the direction of the inclination of its strata, with bleak precipices on the opposite 

 side ; continued oftentimes to a great distance in the line of the direction of the 

 strata. In the pass between Limoux and Alet in the eastern Pyrenees, the strata 

 descend in a line, parallel to the perpendicular aspect, to the banks of the river 

 Aude : the transition rocks present sometimes the same features, particularly 

 in the mountains of the Corbieres. In the latter chain, above the town of St. 

 Paul, the uniformity of disposition is broken by a shift allowing a passage 

 through the chain. The valley of the Corbieres is reached from Mirepoix through 

 a glen, in which the road descends for more than a league at a considerable angle 

 of inclination. It is rendered safe by piled walls of stones ; huge precipices are 

 seen below ; and one or two caverns are met with in the ascent, from which we 

 drove numerous pipistrelles, notwithstanding the proof of fires having lately il- 

 lumed their dark gloom. The great valley, terminating in the horizon's brink, 

 feeding for many miles no stream of magnitude, clothed with alternate fields of 

 vines,-)- of maize, and of olives, presents all the characters of a plain, while on both 

 sides the chains, presenting a bare perpendicular acclivity, descend into the vale 

 beneath, (a fact long ago generalized by Bouguer,) or rear aloft their bare fore- 

 heads in aged majesty. Goats are here the companions of the raven and the 

 eagle ; while oftentimes the bay of the shepherd's dog, disturbing the wolf in the 



• The study of physical geography is yet so novel, that we have been obliged 

 to adopt terms scarcely yet in general use. 



t It is this vale that furnishes the greater part of the excellent Roussillon 

 wine. 



VOL. II. 2 D 



