570 
VAUGHAN MACCAUGHEY 
On the basis of mean temperatures: 
Notably warm i, 4'ai, 4&1. Cool 402, 462, 5. 
Warm 3. Notably cool 403, 4^3, 6, 7, 
3. THE VALLEY FLOOR 
The floor of Manoa is conspicuously broad and flat, much more 
so than are the floors of the valleys immediately adjacent to it, Makiki, 
Pauoa, Palolo, and Waialae. This flatness may be considered as one 
of the evidences of the maturity of this valley. 
The designation "floor" comprehends the region lying below the 
300-foot contour; roughly an area 2.0 miles by .75 mile. It is com- 
posed chiefly of "mountain wash," a heavy, dark reddish-brown, fine- 
textured, adobe soil, that has been washed down from the surrounding 
basaltic ridges and spread out as a deep blanket in the valley basin. 
Along the lower western slopes are extensive deposits of volcanic 
ash and cinders. The thickness of the soil bedding is not known; 
along the center of the valley it must be very deep, perhaps hundreds 
of feet. The red-brown adobe soil is fertile, stiff and intractable in 
cultivation, and exceedingly retentive of moisture. When it becomes 
dry to any considerable depth, as during the infrequent droughts, it 
cracks conspicuously. The cracks are i to 4 inches wide and 12 to 
40 inches deep. 
From an ecologic standpoint the valley floor may be transversely 
divided into two regions, the floor of the lower valley, i. e., near the 
portal, and the floor of the upper valley, near the head. The lower 
floor comprises the area from the portal up to the point at which 
Manoa Stream diverts from the middle of the valley. The upper floor 
continues from this latter point to the region beyond the bifurcation 
of the floor at Puu Pueo. The lower floor is contrasted with the 
upper floor by greater xerophytism; more brilliant illumination; 
higher temperatures of air and soil ; less surface water in the form of 
streams, pools, and springs (although more in the form of irrigated 
taro patches) ; more volcanic material such as surface lava, cinders, 
ashes, etc.; and smoother contours. The upper floor has a higher 
percentage of indigenous vegetation, and in former times was wholly 
covered by the lower forest zone, as will be described in another 
section. 
The valley floor is principally occupied by introduced plants, 
