154 



EARTH FEATURES AND THEIR MEANING 



glaciers " ; though the more generally characteristic are peculiar 

 stripings or other markings which appear upon the surface of the 



_ .,jm^^-^-^^ja^^jiaimiiJ.iiu IIUIIIL. ground and thus betray the 



movements of the underlying 

 materials. Upon slopes it is 

 not uncommon for the surface 

 to be composed of angular rock 

 fragments riven by the frost 



FIG. 159. Striped ground from soil flow 

 of chipped rock fragments upon a slope, 

 Snow Hill Island, West Antarctica (after 

 Otto Nordenskiold). 



FIG. 160. Pavement of hori- 

 zontal surface due to soil 

 flow, Spitzbergen (after Otto 

 Nordenskiold). 



and crossed by broad parallel 

 furrows as though a gigantic 

 plow had gone over it (Fig. 

 159). The direction of the furrows is always up and down the 

 slope, and the striping is marked in pro- 

 portion as the slope is steep. Where the 

 bottom is reached, the furrows are re- 

 placed by a sort of mosaic pavement 

 of hexagonal repeating figures, each of 

 which may be an area of the surface six 

 feet or more across (Fig. 160, and Fig. 

 390, p. 368). The depressions which 

 separate the " blocks " of the pavement 

 are often filled with clay, while the in- 

 closed surfaces are made up of coarsely 

 chipped stone. 



The splitting wedges of roots and trees. In the mechanical 



breakdown of the rocks 

 within humid regions a 

 not unimportant part is 

 sometimes taken by the 

 trees, which insinuate the 

 tenuous extremities of their 

 rootlets into the smallest 

 cracks, and by continued 

 growth slowly wedge even 

 the firmer rocks apart (Fig. 

 161). In a similar manner 

 the small tree trunk grow- 

 ing within a crevice of the 

 rock may in time split its parts asunder (Fig. 162). 





FIG. 161. Tree roots entering fissured rock and 

 prying its sections apart. 



