August 2, 1907] 



SCIENCE 



147 



out. He needs, in short, criteria to guide 

 him where to draw the line. 



The new Tosemite map presents a rather 

 complex problem. Instead of analyzing it and 

 developing the criteria from it, it will be 

 preferable for us to begin by stating the 

 criteria first and then to apply them to the 

 particular case of the Tosemite map. 



A topographic map of any kind, because of 

 its small scale, can not undertake to depict 

 the configuration of the land surface complete 

 in all its details. It is essentially in the na- 

 ture of an abstract, a graphic epitome of the 

 relief. Like any literary abstract, it may be 

 quite brief and confine itself merely to the 

 leading facts; it may be more extended and 

 enter into more or less detail. But whatever 

 its degree of elaborateness, the abridgment of 

 subordinate detail should be evenly main- 

 tained throughout, and, above all, its treat- 

 ment should be complete so far as it goes. 



The main principle then is that a map must 

 tell a story complete in itself. Its scale and 

 contour interval should be so selected as to 

 admit of the full delineation of every feature 

 essential to the story. No irrelevant subor- 

 dinate detail should be included if possible. 



Some concrete examples may be helpful in 

 illustration. 



Let it be required to portray a mountain 

 range in its entirety, with nothing further 

 than its leading characteristics; say a long 

 and narrow block range uplifted along one 

 side, much dissected and enveloped at its base 

 in a broad cloak of waste. These facts may 

 successfully be epitomized by a map on a scale 

 of 1:250,000 with 100 or 200 foot intervals, 

 according to the relief. A smaller scale might 

 leave some of the facts in doubt; a larger 

 scale would introduce superfluous detail. 



Again, let it be required to represent the 

 general character of the sculpture of the range. 

 Suppose the range to have been partially gla- 

 ciated. The new map must be on such a 

 scale as to allow of the distinction between 

 the principal forms of glaciation and those of 

 subaerial erosion. It should be large enough 

 then to admit of the clear delineation of such 

 forms as cirques, arretes, cols, U-canyons, etc.. 



on the one hand, and the characteristic forms 

 of stream and weather erosion on the other. 

 These conditions may be satisfied by a scale 

 of 1 : 100,000 and 100 or 50 foot intervals. It 

 should be noted that this involves a grouping 

 of the land forms into categories of a new 

 sort. Each group constitutes the record of a 

 certain event in the history of the relief of 

 the range. Together the forms of such a 

 group furnish an index of that event, and 

 collectively they may be conveniently referred 

 to as index forms. The index forms of one 

 event are not necessarily all the product of 

 one and the same process, in fact they seldom 

 are. The index forms of alpine glaciation, 

 for instance, include forms of degradation and 

 of aggradation, and so necessarily do those of 

 subaerial erosion. 



If a map then is to tell a complete story, 

 it must aim to show all the essential index 

 forms of one certain event. If it falls short 

 of this it tells the story incompletely; if its 

 scale is such as to admit of subordinate fea- 

 tures, the story is unnecessarily encumbered, 

 and the additional cost of mapping is virtually 

 wasted. 



Finally, let it be required to make a map 

 of a small portion of the range in question, 

 in order to bring out the local happenings by 

 which a certain feature is difierentiated from 

 others of a similar kind. For instance, in the 

 glaciated portion of the range, a certain cirque 

 or canyon may be found possessing decidedly 

 aberrant characteristics. These, being due to 

 local influences, require for their study a map 

 showing the particular index forms in which 

 the incidents due to these local influences may 

 be read. Such a map is the new detail map 

 of the Yosemite Valley (scale 1: 24,000). It 

 aims to represent a glaciated canyon of ex- 

 ceptional form with sufficient detail to shed 

 light on the cause of its aberrant character. 

 Comparison with the standard Tosemite 

 Quadrangle, published several years ago, is 

 interesting in this connection. That sheet, 

 drawn to a scale of 1 :125,000, succeesfully ex- 

 presses the general character of the sculptur- 

 ing of the Sierra Nevada. It shows distinctly 

 the glacial sculpture, on the one hand, and the 



