6 RemarTis on the Formation of Alluvial Deposites. 



gravel, or loaded with boulder-stones. An adventurous traveller, 

 Dr Hugi, states, that it is dangerous to walk at the foot of the 

 Lauteraarhorn, and some other ridges, on account of their ex- 

 treme tendency to decay*. 



Rocks, which fall by these gradual processes, always divide 

 according to their natural structure of separation, and hence 

 every distinct concretion of the rock becomes a separate frag- 

 ment of its debris. 



Two principal forms of mountain masses result from this law. 



The first is that exhibited chiefly by all calcareous and all 

 conglomerate or sedimentary rocks. These are commonly ar- 

 ranged in strata, which approach more or less to an horizontal 

 position, and their cleavages, crossing one another in various di- 

 rections, are nearly perpendicular to the planes of stratification. 

 The fragments, separated from them, continually expose fresh 

 cleavages, and the mountain side exhibits the appearance of vast 

 walls, while its detached summits take the form of mighty tow- 

 ers. These walls can only be ascended by means of the projec- 

 tions of the strata, or of slight inequalities in the cleavages, and 

 hence Mont Blanc itself is more accessible than many Swiss 

 mountains of less elevation, which consist in a great measure of 

 limestone. The debris of these rocks is disposed with great re- 

 gularity at the base of the vertical walls, its largest fragments 

 rolling or sliding to the bottom of the talus ; and the conse- 

 quence is, that such an eminence Is characterized by three prin- 

 cipal lines, viz. the summit of the wall, the summit of the talus, 

 and the base of the talus, — all parallel to the lines of stratification 

 in the rock. 



(The drawing, Plate I. Fig. 1., is designed to show this form. It re- 

 presents part of the Selisberg, on the Lake of Lucerne). 



The second principal form, resulting from the above law of 

 disintegration, is presented by many of the schistose rocks. The 

 strata are in this case highly inclined, and the cleavages meet 

 the planes of stratification at an acute angle. The distinct con- 

 cretions have the figure, often very exact, of rhomboidal crystals. 

 The outline of the mountain mass consists of pointed summits, 

 the form of which resembles that of the distinct concretions. 



• Natur-historische Alpen-reise, 1830, pp. 236, 246, 367- 



