Cairnes — Some Suggested New Physiographic Terms. 85 



The region traversed by the Jvio Grande river furnishes, 

 perhaps, the best example known of the balance between 

 desert and humid conditions. The stream is just powerful 

 enough to overflow from one basin to another and escape to 

 the sea, but it is not strong enough to open up a wide contin- 

 uous valley." Since this stream does get to the sea and carries 

 some sediment, it is to this extent deplanating, but in case it 

 were unable to do so, its activities would be entirely equipla- 

 nating. 



Certain regions that are regarded as uplifted peneplains 

 have, since their uplift, been invaded by inland or continental 

 ice, and consequently glacial plains are there superimposed on 

 peneplains. The region north of the Great Lakes in Canada 

 exemplifies this phenomenon ;f and vast quantities of material 

 thought to have been removed by the ice from the surface of 

 this territory now constitute the drift areas, till plains, 

 moraines, etc., to the south. 



Applanation. 



The material added to a district in the process of applana- 

 tion may be either sedimentary or igneous, and may be water- 

 laid, wind-blown, glacial, or volcanic in character. . 



The sediments everywhere being carried by streams to the 

 sea are deposited within a limited distance of the coast, and 

 tend in time to so accumulate as to rise above the surface of 

 the water ; and at times, a relative lowering of the sea assists 

 in this land-forming process. The coastal plain of the eastern 

 United States is a well-known example of such a surface 

 developed by aggradation and diastrophism. Similar processes 

 are widespread in their operation on the earth's surface. 

 Where the uplift is such that the beds remain horizontal, or 

 nearly so, typical constructional sedimentary plains or appla- 

 nated surfaces result. Yast accumulations of chemical precip- 

 itates, as well as the calcareous and siliceous tests of 

 invertebrates, also are raised above sea-level in places and con- 

 stitute applanated land surfaces. Sedimentation and diastro- 

 phism are thus probably the most important agents producing 

 applanation. 



Wind action, in addition to being a powerful equiplanating 

 and deplanating agent, as described in preceding paragraphs, 

 has also important applanating activities. Recent studies of 



* Hill, E. T., " The physical geography of Texas." 



t Wilson, A. W. G., " The Laurentian peneplain," Jour, of Geol., vol. ii, 

 1903, pp. 611-669. " Physiography of the Archaean areas of Canada," Int. 

 Geog. Congress, Eighth Rep., 1905, pp. 116-135. Bowman, Isaiah, "Physi- 

 ography of the United States," in Forest Physiography, 1911, see pp. 554- 

 568. Martin, Lawrence, " Physical geography of the Lake Superior region," 

 U, S. Geol. Surv., Mon. lii, 1911, pp. 85-112. 



