PHYSIOGRAPHIC PROBLEMS OF TODAY 543 



gist, but, on passing to the secondary feature, the influence of Hfe 

 becomes apparent, and the relation of man to nature is in the end 

 the leading theme. 



SECONDARY PHYSIOGRAPHIC FEATURES. 



The most familiar features of land areas, as is well known, are. 

 those which owe their existence to the work of moving agencies 

 resident on the earth's surface, such as the wind, streams, glaciers, 

 waves, currents, etc. The forces at work are set in motion by energy 

 derived from without the earth, and the material worked upon is 

 brought within the range of their activities by forces resident within 

 the earth which cause deformations of, or additions to, its surface. 

 The earth-born primary physiographic features are thus modified 

 by sun-derived forces, and a vast array of secondary modifications of 

 relief are produced which give variety and beauty, particularly to 

 those portions of the lithosphere which are exposed for a time to the 

 air. The study of secondary physiographic features has produced a 

 rich and abundant harvest, especially during the last quarter of a 

 century, and the returns are still coming in with seemingly an accel- 

 erated rate. 



The themes for study are here mainly the various processes of 

 erosion and deposition of the material forming the outer film of the 

 lithosphere, and the characteristics of the destructive and constructive 

 topographic forms produced. With the knowledge gained concerning 

 the changes now in progress on the ocean's shore, in the forest, by 

 the river side, on the snow-clad and glacier- covered mountains, etc., 

 the physiographer seeks to decipher the records made in similar situa- 

 tions during the past. Two groups of problems are in sight in this 

 connection ; one is concerned with observing, classifying, and recording 

 the changes now in progress ; and the other has for its chief aim the 

 translation, in terms of the agencies now at work, of the records left by 

 past changes. We find that today the same area is being inscribed 

 perhaps in several different ways. The surface of the earth, like an 

 ancient manuscript, is frequently written upon in difterent directions, 

 and with different characters. It is the duty of the physiographer 

 to translate this ancient pahmpsest, and deduce from it the history 

 of the development of the features of the earth's surface. It has 



