PHYTOGEOGRAPHY OF MANOA VALLEY, HAWAIIAN ISLANDS 58 1 
volcanic ejecta. There are a number of lesser, unnamed craters on 
the west ridge, and on the lower valley floor, which are very obscure, 
and not of phytogeographic significance. 
The three named craters in prehistoric times discharged vast 
quantities of volcanic ashes and cinders. This material was deposited 
in thick blankets over the local topography, obliterating the original 
land features, and masked the irregularities which had been produced 
r 
Fig. 8./ View on the slopes of Round Top, showing garden patches, papaia trees 
and general physiography. 
by erosion. Thus the surface of the Roundtop Foothill is much 
smoother than that of the Manoa-Palolo foothill. On the latter the 
surface material is the ponderous basaltic sheet lava of which the 
original volcanic dome was composed ; on the Roundtop foothill the 
surface material is a secondary volcanic product — lapilli — light in 
weight, very porous, and produced within relatively recent geologic 
times. 
This difference in the nature of the surface material has resulted 
in a striking difference in the agricultural utilization of the two foot- 
