1917] MACCAUGHEY—HAWAIIAN FLORA 419 
high show ages of 30 to 4o years; trees 15-20 ft. high, ages of 50 to 
7° years; and trees of 40-60 ft. high, ages of 100 to 200 years or 
older. It may be stated as a general conclusion that the ligneous 
plants of the lava flows, like those of other deserts, attain great 
age and assume the aspect of senility at an early period in their 
lives. 
Fossil trees 
When a lava flow rolls down the mountain slope it may, and 
commonly does, meet with a grove or woodland across its path. 
The varying results of the encounter may be summarized as follows: 
1. The forest may be entirely consumed by the lava flow, the 
trees beaten down and burned, and all trace of the grove wiped 
out by the rock sheet. This usually happens if the flow is a-a 
and is quite thick. There is abundant evidence on the slopes of 
Loa, Kea, and Haleakala to show that hundreds of thousands of 
acres of beautiful woodland have been obliterated by lava flows 
within comparatively recent geological time. 
2. The flow, if of the pa-hoe-hoe type and moving quite rapidly 
through the grove, may only destroy the foliage, brushwood, and 
lesser vegetation. The large tree trunks are resistant even to the 
great heat of the flow. Moreover, the surface lava cools with such 
extreme rapidity (this is a noteworthy feature of the Hawaiian 
lavas) that the radiation from within is relatively slight. In this 
way large trunks are coated with an envelope or shell of lava which 
quickly cools and hardens, and forms a protective case, so that the 
heat from adjacent liquid lava does not reach the tree. The main 
mass of the lava flows on down the slope, leaving the grove spattered 
and jacketed with lava. Often great blobs of lava remain clinging 
to the larger limbs and festooning the summits of the saplings. 
Remnants of woodlands, exhibiting these phenomena, are not 
uncommon on the lee slopes of Loa. . 
3. The lava flow, acting under conditions like those just de- 
scribed, but moving more slowly, may ensheath the trees to a con- 
siderable height, for example, 20 ft. A jacket is formed as has been 
described, but the gradual incineration of the outer layer of wood 
results in a space between the tree trunk and the lava jacket. 
Fresh lava, under pressure, will force its way into this space, and 
