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r9ro] LIVINGSTON—SOIL MOISTURE 253 
with the high soil moisture content (almost 11 per cent) and the 
high percentage of the moisture-retaining power (almost 23 per 
cent) which this soil exhibits during the driest month of the year. 
It is to be remembered in this connection that the soil of the hill 
is often considerably over 30 cm. in depth, and that, in the dry 
season, the highest moisture content is to be expected just above 
the underlying rock surface. In the summer of 1904, immediately 
preceding the advent of the July rains, a soil sample from a depth 
of 35 cm. on the hill exhibited a moisture content of 17.9 per cent 
of its dry weight. From the graph of the hill soil and from this last 
consideration may be derived convincing additional evidence in 
favor of the conclusion expressed by SPALDING and by the author 
(Publication 50, Carnegie Inst., p. 12) “that sufficient moisture 
is probably at all times present in the deeper layers of these soils 
[of the hill] for the needs of transpiration and even growth.” The 
excellent soil conditions exhibited by Tumamoc Hill are emphasized 
by the fact that at no time during the period of record did the 
observed moisture content at a depth of 30 cm. fall below 8.9 per 
cent, and that it was far above 11 per cent at all times excepting 
in the months of June and November 1908. 
The soil of the Larrea slope, at a depth of 20 cm., just above 
the caliche hardpan, exhibited only 3.1 per cent of moisture as the 
June average. Had the soil been sifted, the moisture content 
would undoubtedly have been markedly greater, as is indicated 
by the high percentage of its retaining power (15.5 per cent) 
which the moisture content represents. But the amount of water 
available for plants must be considered as a vanishing quantity at 
this time. 
In this vicinity, practically the only perennially active plant 
on the slope, excepting a few scattered cacti and here and there a 
Plant of Fouguieria (itself hardly perennially active), is the creosote 
bush, from which the slope is named. This plant, as has been 
mentioned, is probably the most resistant to drought conditions 
of all non-storage forms in the region. An inspection of the graph 
for this soil brings out the fact that the moisture content rose 
: _ above ro per cent only in February and March, in July and August 
1908, and in the winter of 1909. In distinct opposition to the soil 
