Ice and its Natural History 279 



modified by the secondary effect of running water. This 

 modification is equivalent to intensification, in so far as the 

 running water, by removing the products of decomposition, 

 and thus denuding the rock, exposes fresh surfaces to the 

 decomposing agency. 



In its simplest and most perfect form the effect of chemical 

 and gravitational degradation, which has been active through 

 all the ages that a distinctly tropical climate has existed, is to 

 be witnessed on the prairie and the pampa. 



Here the wayfarer finds himself on a surface as feature- 

 less as the ocean, but equally spherical ; and he may use his 

 horizon for the purpose of finding his position astronomically 

 with almost as much confidence as he would at sea. 



Water finds its level quickly ; sea-ice, slowly ; land-ice, 

 more slowly ; and land, in a time which, though very great, 

 is still far from infinite. 



