174 Penck — Climatic Features in the Land Surface. 



in other regions of the earth, and further research will help us 

 to establish the general rule of all their climatic oscillations, 

 and we shall understand them the better the greater our 

 knowledge of the surface forms. 



The forms of the earth's surface are very complex things. 

 In the beginning of geological research it was generally main- 

 tained that every rock had its peculiar forms, and still to-day 

 some text-books contain pictures of granite or sandstone moun- 

 tains. Later, it was believed that every kind of structure of 

 the earth's crust assumed its own surface features, and struc- 

 tural geology was regarded as the very content of geomorphol- 

 ogy. Later still was recognized the importance of the different 

 exterior processes which shape the earth's surface, and there are 

 still many differences of opinion as to their effects. It is only 

 recently that the full importance of time has been observed for 

 the development of surface features. After having seen how 

 different the forms are which come into existence in a natural 

 sequence under the control of a certain process, as shown by 

 the geographical cycle, we can fully appreciate the differences 

 of iluviatile, glacial and desert forms, and we shall have thus 

 gained the possibility of such a close examination of forms that 

 we can read their history. 



This study of erosional forms can be supplemented by that 

 of corresponding deposits. We now easily separate river 

 deposits from moraines, which in the beginning of scientific 

 research have been taken for the results of large floods. It is 

 also possible now to distinguish the deposits of different phases 

 of a geographical cycle from one another, and the variegated 

 or impoverished composition of gravel deposits allows con- 

 clusions as to the surface features which prevailed during their 

 formation. We do not doubt that continued observations of 

 desert deposits will result in the establishment of sharp dis- 

 tinctions between them and fluviatile deposits, though it is not 

 easy to distinguish between deposits of young rivers of a plu- 

 vial climate and those of mature rivers of a desert climate. 

 Thus the study of deposits may afford us a crucial test as to the 

 result of our study of forms. 



Forms are always in the way of evolution ; where destruc- 

 tion prevails on the land surface the existing forms are always 

 in process of destruction ; only where they are buried under 

 new deposits are they conserved. The surface of every layer 

 deposited on the land has been an old land surface. Thus the 

 study of deposits also reveal forms of the past, and if we are 

 accustomed to interpret the meaning of forms and deposits, we 

 can read far older climatic conditions in deposits than are 

 exhibited in the existing surface features of the land. 



