502 Notes on the Pyrenees. 
he does not, however, seem to have seen the geognostic 
cause; as the junction of one valley or more generally takes 
place in a basin, and the extent of the latter is proportioned 
to the number and to the size of the outlets which terminate 
in it. 
The sum of the maximum of elevation of the crest marked 
in the peaks or culminating points, and of the minimum 
marked by the transverse valleys and cols, ports or passages, 
gives the mean height of the crest chain of hills. “The deter- 
mination of the mean height of the line of the crest by the 
mean height of the cols, ports, or passes, is, even accor ding to 
the Baron de Humboldt, an abstract idea, and vague fect 
there is grouping of mountains and no continuous chain; ; and 
I think that a nearer approximation would be gained to the 
mean height of the crest by a comparison of the maximum 
and minimum of elevation of the protuberances themselves, 
than by a hasty calculation founded upon the height of such 
ridges or passes, whose depths are oftentimes connected 
with accidents posterior to the formation of the chain. Some 
countries of mountains, as the Himmaleh, are traversed by 
large rivers; chains (dovre-feldt, &c.) are often divided by 
profound rents, which are sometimes empty veins (Jameson, 
Von Buch); while the basin of the crest may, in other cases, 
be filled with deposits of the coal formation or other secondary 
or more modern deposits (Alps, Lebau). ‘The data upon 
which the calculation of the mean height of the crest of the 
Pyrenees has been founded are more or less empirical ; for 
the country of mountains known under that name consists of 
aseries of parallel and lateral chains, from which the principal 
is oftentimes difficult to be distinguished. When a country 
of mountains, as the Grampians for example, consists not of 
one continuous crest, but of a series of crests, more or less 
parallel to one another, traversing the country at angles to 
the line of the direction of the chain, the data of the calcula- 
tion should be founded on the mean height of the culminating 
points and minimum of crest in each chain, which alone can 
give the mean height of the whole range ; and in this case the 
transv erse or divergent chains should be entirely neglected. 
From the disposition of countries of mountains, and one which 
appears common, some apparent anomalies take place: thus, a 
chain that is divergent, and transverse to the chain whose 
crests are to give the data for the calculation of the mean 
height of the range, may be parallel to the line of that range 
which is at right angles to the principal crest. Charpentier 
has remarked, in the Pyrenees, that the point of departure 
of transverse or lateral branches from the main or from 
