ON THE DECLIVITIES OF MOUNTAINS. 263 



Where mountains interfect each other in an oblique direc- Mountains near 

 tion, the N. E. fide of one range being contiguous to the " t c e h rc e th t e ^' 8 ° uld 

 S. W. flanks of another range, there the afflux of adventitious depofi tion. 

 particles on the north-eaft tide of the one, muft have fre- 

 quently extended to the S. W. fide of the other, particularly 

 if that afflux were ftrong and copious; thus the Erzgebirge of 

 Saxony, which run from W. to E. have their N. E. fides con- 

 tiguous to the S. W. fide of the Riefengebirge that feparate 

 Sileiia from Bohemia, and hence thefe latter are covered with 

 the fame beds of gneifs, &c. as the northern fides of the Saxon, 

 and thereby are rendered finooth and gentle comparatively to 

 the oppofite fide, which being fheltered, remains fteep and 

 abrupt, which explains the feventh obfervation. 



The caufes here affigned explain why the covering of ad- Ifc W0U U '■* leaft 

 ventitious ftrata on the higheft mountains is genecally thinneft hetehtf ' fc'c? 

 at the greateft height, and thickefl towards the foot of the 

 mountain, for the bulk of the water that contained the adven- 

 titious particles being proportioned to its depth, and the mafs 

 of earthy particles with which it was charged, being propor- 

 tioned to the bulk of water that contained them, it is plain, \ 

 that as the height of water gradually decreafed, the depofitions 

 from it on the higher parts of the mountains muft have been 

 lefs copious than on the lower, where they mufl; have been - 

 oftener repeated. 



Hence, 2. granitic mountains, generally the moft ancient, 

 frequently have their northern or eaftern fides covered with 

 ftrata of gneifs or micaceous fhiftus, and this often with ar- 

 gillite, or primaeval fand-ftone, or lime-ftone, thefe being 

 either of fomewhat later formation or longer fufpendible in 

 water. 



Hence, 3. different fpecies of ftone are often found at 

 different heights of the fame flank of a mountain, according 

 as the water which conveyed thefe fpecies, happened to be 

 differently impregnated at different heights ; during the firfl 

 iera its depofitions formed the primitive ftony maffes, but after 

 the creation of fifti, lime-ftone, fand-ftone, farcilites and fe- 

 condary argillites, in which pifcine remains are found, were 

 depofited. But during the fecond sera, viz. that of the No- 

 achian deluge, by reaforv of the violence and irregularity of 

 its aggrefflon, the depofitions were more mifcellaneous and 

 axe found at the greateft heights ; yet in general they may 



well 



