544 T. C. CHAMBERLIN — CHRONOLOGIC CARTOGRAPHY. 



To distinguish between a plain and a peneplain which may be quite rolling 

 and yet clearly determinable, continuous lines may be used for the former 

 and broken lines for the latter. The glacial surfaces may be represented by 

 parallel wavy lines where they are approximate plains, and by discontinuous 

 wavy lines where morainic or broken. Where desirable, the character of the 

 wavy lines may be modified so as to imitate in some degree the undulations 

 of the topography. Lava plains may be represented by checks, and delta 

 fans by diverging lines consonant with their formations. Folds may be rep- 

 resented by a succession of arched lines like the old "caterpillar" conven- 

 tion for mountains, but of course in appropriate color, and. faulted and tilted 

 plains by a succession of angulated lines imitating the displacement. 



These are devices for genetic representation. To introduce the chrono- 

 logic element, it is proposed that colors be used corresponding to the periods 

 to be indicated, each period to have a single color, in which its subaerial 

 plains shall be represented by parallel lines ; its fluvial plains by arrow- 

 headed lines pointing shoreward ; its glacial plains by wavy lines ; its slopes 

 by dots, etc. 



