80 THE ATMOSPHERE — FROST 



cordance with the arrangement of the more and less durable 

 layers. When the harder beds are at the top, flat-topped tables, 

 or mesas, with steep sides, are carved out ; when this hard bed is 

 removed, or was not originally present, rounded and dome-shaped 

 hills and high, narrow, and precipitous buttes result, with the more 

 durable layers cropping out on the sides as projecting ledges. 

 Isolated hard patches, by protecting the softer beds beneath them, 

 gradually cause the formation of pillars, as the unprotected por- 

 tions are cut away, and these pillars may be observed in all stages 



FlG. 24. — Bad-land peak, South Dakota. The horizontal stratification is very 

 plainly marked. 



of their formation. Monument Park, in Colorado, is especially 

 noted for this feature. Eventually the hard cap of the pillar 

 becomes undermined and falls, and then the shaft is speedily 

 removed. 



2. Frost 



The term frost, in this connection, is restricted to the freezing 

 of water. Water is one of the comparatively few substances which 

 expand considerably on passing from the liquid to the solid state. 

 This expansion, which amounts to about one-eleventh of the 



