[ 36 ] 



But to diftinguilh caufes of the former clafs from thofe whofe'- 

 operation was more confined, it is neceffary to difcover fome 

 charadler by which their effeds may unequivocally be difcerned. 



Now a general uniformity, or agreement in fome particular cir- 

 cumftance in every pai-t of the globe, feems to be a fure teft of 

 the operation of fome general caufe. The difcovery of uniform 

 appearances is therefore of primary importance in geological re- 

 fearchee. In the prcfent effay I fhall confine myfelf to the in- 

 veftigation of one inftance of this fort, namely, the inequality of 

 declivity which the iides or flanks of mountains exhibit in every 

 part of the globe hitherto examined according to the points of. 

 the compafs to which they face, and are expofed. 



That one part of almoft every high mountain or hill is fteeper 

 tfcan another could not have efcaped the notice of any perfon 

 who had traverfed fuch mountains, but that nature in the for- 

 mation of fuch declivities had any regard to different afpeds or 

 points of the compafs, feems to have been firft remarked by the 

 celebrated Swedifh Geologift Mr. Tilas in the 22d vol. of the 

 Memoires of Stockholm for 1760.* Neither Varenius, Lulolph 

 nor Buffon in his Natural Hiftory publifhed in 1748, have noticed 

 this remarkable circumftance. 



The 



* See alfo vol. 25, Swed. Abhandl. p. 291, where Cron/led exphins fome ob- 

 ieure parts of Tilas's obfervation. 



