STUDIES IN THE SIERRA* 

 By John Muir 

 NO. VI. — FORMATION OF SOILS 



NATURE has plowed the Sierra flanks more than a mile 

 deep through lava, slate, and granite, thus giving rise to a 

 most lavish abundance of fruitful soils. The various methods 

 of detachment of soil-fragments from the solid rocks have 

 been already considered in the foregoing studies on glacial and 

 post-glacial denudation. It now remains to study the forma- 

 tion of the variously eroded fragments into beds available for 

 the uses of vegetable life. 



If all the soils that now mantle the Sierra flanks were spread 

 out in one sheet of uniform thickness, it would measure only a 

 few feet in depth, and its entire removal would not appreciably 

 affect the configuration of any portion of the range. The larg- 

 est beds rarely exceed a hundred feet in average thickness, and 

 a very considerable proportion of the whole surface is naked. 

 But we have seen that glaciers alone have ground the west 

 flank of the range into soil to a depth of more than a mile, 

 without taking into account the work of other soil-producing 

 agents, as rains, avalanches, torrents, earthquakes, etc. It ap- 

 pears, therefore, that not the one-thousandth part of the whole 

 quantity of soil eroded from the range since the beginning of 

 the glacial epoch is now left upon its flanks. 



The cause of this comparative scantiness of the Sierra soil- 

 beds will be readily apprehended when we reflect that the gla- 

 cier, which is the chief soil-producing agent, no sooner de- 

 taches a soil-fragment than it begins to carry it away. During 

 the long glacial winter, soil-material was poured from the 

 range as from a fountain, borne outward by the mighty cur- 

 rents of the ice-sheet to be deposited in its terminal moraines. 

 The only one of these ancient ice-sheet moraines which has re- 



* Reprinted from the Overland Monthly of December, 1874. The author's revisions 

 and corrections have been incorporated from a copy of the article found among his 

 papers. — The Editors. 



