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 according to 

 the Baron de Humboldt, an abstract idea, and vague when 

 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 

 a series 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 

 transverse 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 later«al branches from the main or from 



