SUPPLEME]^T. 



The advance made in the study and in the interpretation of the meaning 

 of topographic forms, has been so great, especially in America, during the 

 present decade, that I am sure the reader will be interested in the writings of 

 those who have made this important departure from old methods. The recog- 

 nition that lakes are transient features of the ever-changing earth's surface and 

 come and go during cycles of topographic development, was first clearly set 

 forth in a brief paper by "W. M. Davis, ^ which is here reproduced. 



The Classification of Lakes. 



Several years ago I presented to the Boston Society of Natural History a 

 paper on the classiiication of lake-basins, in which the many varieties of lakes 

 were grouped under three heads, according as they were made by constructive, 

 destructive, or obstructive processes. The first heading included lakes made 

 by mountain-folding and other displacements ; the second consisted chiefly of 

 basins of glacial erosion ; the third contained the greatest number of varieties, 

 such as lakes held by lava, ice, and drift barriers, delta and ox-bow lakes, and 

 some others. The classification proved satisfactory, in so far as it suggested 

 a systematic arrangement of all kinds of lakes that have been described ; but 

 it now appears unsatisfactory, inasmuch as its arrangement is artificial, with- 

 out reference to the natural relations of lakes to the development of the drain- 

 age systems of which they are a part. A more natural classification is here 

 presented in outline. 



When a new land rises from below the sea, or when an old land is seized 

 by active mountain-growth, new rivers establish themselves upon the surface 

 in accordance with the slopes presented, and at once set to work at their long 

 task of carrying away all of the mass that stands above sea-level. At first, 

 before the water-ways are well cut, the drainage is commonly imperfect : 

 lakes stand in the undrained depressions. Such lakes are the manifest signs 

 of immaturity in the life of their drainage system. We see examples of them 

 on new land in southern Florida; and on a region lately and actively dis- 

 turbed in southern Oregon, among the blocks of faulted country described by 

 Kussell. ]')Ut as time i)asses, the streams fill up the basins and cut down tlie 

 barriers, and the lakes disappear. A mature river of uninterrupted develop- 



1 Science-, vol. 10, 1887, pp. 142, 14:J. 



