GEOLOGY: C. KEYES 
33 
indicated with some certainty by the comparison of photographic and 
photovisual magnitudes, it is of interest to find it appearing as the 
result of an entirely different method of investigation. 
The absence of faint white stars is known to be a characteristic of 
other regions as well,^ but it must not be inferred that such objects are 
not to be found anywhere in the sky. In Selected Area No. 88, for 
example, in one of the outlying clouds of the Milky Way, photographs 
by the exposure-ratio method indicate that the stars of the 14th or 15th 
magnitude are nearly normal in color and thus include a considerable 
number of objects that are white. Mr. Shapley has also accumulated 
evidence of this sort in connection with his study of clusters. 
1 These Proceedings 2, 1916, (521-525). 
^Astroph. /., Chicago, III., 39, 1914, (361-369); [Mt. Wilson Contrib., No. 81]. 
^Ibid., 40, 1914, (187-204), 42, 1915, (92-119), (120-132); [ML Wilson Contrib., Nos. 83. 
100, 102]. 
TERRACING OF BAJADA BELTS 
By Charles Keyes 
Communicated by W. B. Clark, December 16, 1916 
For the local stream-trenching and the resultant terracing of the 
higher zones of those long uniform slopes which so often spread out 
from the foot of desert mountain ranges there is an explanation very 
much simpler than any of the numerous ones yet offered. It has the 
advantage of being in strict accord with the regular and ordinary phases 
of erosional action which recent critical observation shows to be now 
at work as vigorously and as effectively as they have been in any past 
period. It is, in effect, nothing more than a reiteration, in a somewhat 
new form to be sure, of the old law of parsimony which forbids the 
unnecessary multipHcation of explanatory elements and agencies. 
In all late physiographical writings in which the term bajada is used 
it is unfortunately misconstrued. Spanish-speaking Americans do not 
seem ever to have given the title so broad a meaning as that some- 
times attached to it. If the name is to remain a useful geographical 
term of description it should be allowed to retain something of its 
original significance, and should be restricted in its application to the 
steeper slopes of the desert piedmonts. Without exception bolsons 
appear to present four distinct physiographic areas, or belts, three of 
which are plains. There is the central, more or less level tract, some- 
times covered for a period of a few days or weeks of each year by a 
