1917] MacCAUGHEY—HAWAIIAN FLORA 403 
monument at the place of discharge. Cones of this sort are plenti- 
ful on the slopes of Loa and Kilauea. From this outlet the lava 
begins its journey down the slopes of the mountain. The surface 
quickly freezes over and produces a tunnel, beneath the roof of 
which the fluid lava flows with comparatively slow further loss 
of heat. It empties its own tunnels, and in this way the long lava 
tubes, beneath the flows, are formed. The great lava streams 
that flow down the side of Loa sometimes attain a length of nearly 
50 miles, and occasionally enter the sea. They are often 2 or 3 
miles broad. DANA estimated the 1852 flow to contain over 
10,500,000 cu. ft. of lava. The low angle of slope presented by 
the flanks of the mountain, and its nearly flat summit, are due to 
the tendency of the sheet of liquid rock to travel far and spread 
widely before cooling. It is by the successive additions of such 
sheets that the mountain has been built up. 
It is of interest to note RussELu’s® statement concerning the 
great Columbian lavas of the Northwest, which cover an area of 
200,000-250,000 sq. miles. He points out that this is “not one 
vast flow, but is composed of many independent sheets, which 
are sometimes separated by land surfaces containing the stumps 
of trees and even huge trunks buried in lapilli and now thoroughly 
silicified.”’ 
SURFACE OF LAVA FLOWS.—There are two principal types of 
lava forming the Hawaiian flows, which determine the general 
surface and structure of the flow: Pa-hoe-hoe, the native word for 
smooth or shining, designates the smooth pavement type (figs. 
14-17). The crust is glassy and frequently quite brittle. Hum- 
mocks or mounds are frequent, due to the rapid cooling of the sur- 
face. Some of these mounds are quite small, others may be 
30-40 ft. high and twice as long, the thick crustal layers being 
broken and heaped like “pack ” ice. The surface of the pa-hoe-hoe 
is commonly of a ropy or festooned pattern. The wrinkles and 
furrows have their convex arcs downstream, as the velocity is 
greater in the center than at the sides. As the smoother, pavement- 
like parts of the flow cool, vertical cracks develop in every direc- 
tion, forming a coarse network or mosaic pattern. The distance 
8 Russet, I. C., Volcanoes of North America. Macmillan. 1897 (p. 250). 
