8 Remarks on the Formation of AUuvial Deposites. 



masses which have been described, are in nature strongly con- 

 trasted, and usually characterize the rocks to which I have as- 

 signed them. 



In illustration of these preliminary processes, I shall only fur- 

 ther observe, that, in the highest mountains, the loosened earth 

 and stones fall upon masses of ice and snow, which carry them 

 many miles, and that, having been transported from their source, 

 they descend by their own weight into such slopes as have been 

 delineated. 



(9b all no 



II. — On the Distribution of Debris by Streams fiorving over inclhied' or 

 level surfaces. 



Fragments of rock and masses of earth, falling by their own 

 weight, rest in a steep slope. If the force of running water be 

 united to their weight, it carries them much farther, so as greatly 

 to diminish the steepness of the slope. Hence, if a ravine dis- 

 charges water as constantly as earth and stones, instead of an 

 acute cone of debris we see a cascade, which forms a basin 

 within the debris, and then a ravine across it; and through this 

 channel the torrent continually discharges both its water and its 

 solid contents. In such cases the form of the Acute Cone is al- 

 most obliterated by the removal of its upper and more charac- 

 teristic portion. (See the sketch. Fig. 4.) But the lengthened 

 talus, so commonly found at the base of calcareous, sedimentary, 

 or trap-rocks, retains its form, except that it is scalloped or in- 

 dented by a ravine under each cascade. (See sketch. Fig. 5.) 



The mass of debris is, however, chiefly acted on, not by water 

 thus accompanying it in its fall, but by streams meeting it trans^ 

 versely. The materials carried, to borrow an expression from che- 

 mistry, in the dryway, and disposed into the form eitherof a talusj 

 or an Acute Cone, or perhaps originating in a landsHp or in an 

 earthquake, commonly fall down the sides of some glen or val- 

 ley, at the bottom of which flows a torrent. The torrent, fed 

 by numerous cascades, springs, and rivulets, exerts upon the 

 base of these masses a force proportioned to its depth and ra- 

 pidity. Then, first, the angular fragments begin to be rounded 

 into boulder-stones and pebbles. By continually rubbing, grind- 

 ing, and beating upon one another, and upon the sides of their 



