ON THE DECLIVITIES OF MOUNTAIN^ 257 



Memoirs of Stockholm for 1 760 *. Neither Varenius, Lulolph 

 nor Buffon in his Natural Hiftory publifhed in 17 43, have no- 

 ticed this remarkable circumftance. 



The obfervation of Tilas however relates only to the ex- The deep fide 

 treme ends, and not to the flanks of mountains ; with refpeft ******* ^Tila*. 

 to the former, he remarked that the Jieepcft declivity always 

 faces that part of the country where the land lies loweft, and 

 the gentlejl that part of the country where the land lies higheft, 

 and that in the fouthern and eaftern parts of Sweden they con- 

 fequently face the E. and S. E. and in the northern the W. 

 The effential part of this obfervation extends therefore only 

 to the general elevation or deprefiion of the country, and not 

 to the bearings of thefe declivities. 



The difcovery that the different declivities of the flanks of The weftern 

 mountains bear an invariable relation to their different afpects, gjemasmf * 

 feems to have been firft publifhed by Mr. Bergman in his 

 phyfical defcription of the earth, of which the fecond edition 

 appeared in 1773. He there remarked that in mountains that 

 extend from N. to S. the weftern flank is the fteepeft, and the 

 ^aftern the gentleji. And that in mountains which run E. and 

 W. the fouthern declivity is the fteepeft and the northern the 

 gentleft, vol. 2d. § 187. 



This affertion he grounds on the obfervations related in his Inftances.^ In 

 firft vol. § 32, namely, that 1° in Scandinavia the Suevoberg Scandina ™' 

 mountains that run N. and S. feparating Sweden from Norway, 

 the weftern or Norwegian (ides are the fteepeft, and the eaftern 

 or Swedifh the moil moderate, the verticality or fteepnefs of the 

 former being to that of the latter as 40 or 50 to 4 or 2 f. 



2dly. That the Alps are fteeper on their weftern and fouthern The AIp«. 

 fides than on the eaftern and northern. 



3dly. That in America the Cordelieres are fteeper on the The Cordeliere*. 

 weftern fide, which faces the Pacific Ocean, than on the eaftern. 

 But he does not notice a few exceptions to this rule in parti- 

 cular cafes which will hereafter be mentioned. 



Buffon, in the firft vol. of his Epochs of Nature publifhed in Remark* of 

 1778, p. 185, is the next who notices the general prevalence Buffon > 



* See alfo vol. 25, Swed. AbhandL p. 291, where Cronfted ex- 

 plains fome obfcure parts of Tilas's obfervation. 



f The verticality of the fides is inverfely as the length of the 

 defcent. 



Vol, IV.— April. S of 



