504 Notes on the Pyrenees. 
the Andes to the culminating points of the Pyrenees, and in 
the Himmaleh to the culminating points of the Alps. From 
considerations founded on the same data, the relation of the 
mean height of minimum of crest to the culminating point 
would be in the Pyrenees as 1: 1°4; in the Alps as 1:2; in 
the Andes as 1: 1°8; in the Venezuela as 1: 1°8; in the Cau- 
casuS as 1:2; in the Alleghani as 1: 1°8; in the Himmaleh 
as el:8: 
Considerations founded on a physical conception of the 
height of chains, which will improve as the facts connected 
with their physical laws will be more perfectly developed, 
are of the highest interest to the oryctography of the earth. 
The graphic sections used by De Humboldt in his delinea- 
tions of the Andes, by Parrat and Engelhardt in the Cau- 
casus, by Wahlenberg in the Alps of Switzerland and the 
Carpathians, by Schublers and Hoffmann in France, by 
D’CEynhausen and Deehen in the Capitania de Minas 
Geraes, by D’Eschwege in the plains of Mysore and the 
gates of Malabar, and by the engineering officers attached 
to the survey of Major Lambton in India, and which are 
founded on simple barometric or geodesical operations, have 
been of much utility in obtaining conclusions of this nature. 
The Marquis La Place, led to consider that the surface of 
the earth, when liquid, would be pretty nearly in a state of 
equilibrium, from the harmony which experiments on the 
pendulum offer with the results given by the mensuration of 
terrestrial degrees and with the lunar inequalities, remarks, 
that as it would follow from this agreement that the mean depths 
of the sea might be of the same nature as the height of con- 
tinents and islands it must be evident that the mean height 
bears little connection with the culminating points of moun- 
tain chains, while the mean height of the cr ests forms an indis- 
pensable accessary to the evaluation ; and, as De Humboldt 
has remarked at greater length, the chains and mountains 
which attract the curiosity of the vulgar have much less 
importance in such considerations than the vast plateaux, and 
undulating plains, and alternating slopes, which influence, by 
their extent and their mass, the position of the mean surface ; 
that is to say, upon the height of a plane so placed, that the 
sum of the positive ordinates are equal to the sum of the 
negative ordinates. 
There are other more or less impor tant phenomena 
attached to the geography of mountain chains, and among 
these their external aspect and outline form interesting fea- 
tures, when from the ramparts of Montauban we fir St com- 
mand that vale, or rather plain, which extends on one side to 
