Meee. we ee eee 
426 
Slightly higher terraces where the surface wash of the slopes adjoining 
them has been deposited, exhibit the best conditions for growth. However, 
such terraces are narrow. On the gentle slopes, with a gradient of 20° 
and under and on top of the level ridges, good vegetation conditions are 
obtained. 
The soil, as-already shown, is composed of a heavy. clay, the residual 
of the andesitic rocks of the mountain. The depth, even on rather steep 
slopes, is surprisingly great. All through the formation, holes in many 
instances 2 meters deep made by Negritos in search of the wild yam occur. 
In some instances the residual soil on narrow level ridges is as much 
as 3 meters in depth and perhaps more. In many places, however, the 
disintegrated portion of the rock is at or near the surface; in such 
places the vegetation is thin. Here deciduous or evergreen trees with 
xerophytic structures are common. ; 
An analysis *° of soils collected on the tops of ridges and on terraces | 
shows the following: 
TasLe XVI. 
| es uaEaty | 
H,O | Loss on | | 
\ Pol keds | | + Water 
| | 105°. | ie. | oe | Ses 8. | a ee HUmUus. | capacity. 
Pensprts OE Ses: Cbegisegs eee SS SR aie ed 
Per ct. Per ct, | Per ct, | Per ct. | Per ct. Per ct. | Per ct.| Per ct. | Per et. | 
| abr tS | 6.98 11.89) 0.12 0.06| 0.083; 0.11) 0. 3.99 54.06 
3 pera Megiee ves Fa Sh | 7.50 13.36 26) .08 12)  .09 .20| 2.77) 56.71 
gan cae aN | 6.99 8.45| 1.05; .07| 15 | yw! 98) 2,98) 51.92 
PV ster | 6.34 11.29) .2 a8 | ee 51 wot 51.30 
| | } 
Description of soils.—I is the surface soil of a ridge; II, collected at 
depth of 15 centimeters in the same situation; III and IV are surface 
soils collected from terraces. 
Humus.—lIt will be seen that the soils are not deficient in essential 
elements and that the water-holding capacity is high. The absence of 
humus in the soil of tropical forests has long been a subject for discussion. 
Schimper,** quoting Wohltmann, claims that humus covers smaller areas 
in the Tropics than in temperate zones. In South India, however, about 
one-third the area is covered with a rich soil containing 8 to 9 per cent 
of organic matter. The analyses of the soils in question show an aveteae 
humus content of 3.09 per cent, which in comparison with twenty soils * 
given by Stockbridge is rather high. Of the twenty which he mentions, 
the Lamao soils are surpassed by only three. Nevertheless, in comparison 
“ All soil analyses given in this paper were made by L. A. Salinger of this 
Bureau. The methods for chemical analysis are those adopted by the Association 
of Official Agricultural Chemists. See Bull. 46 (revised edition), U. 8. Dept. of 
Ag. Div. of Chem. Water capacity, loss on ignition, humus, and loss of water at 
100°-105° are calculated on air-dry soil. 
“ZL. c., 380. 
“ Stockbridge, H. E. Rocks and Soils, 250, 1895. 
