.} 
INTRODUCTION. XXI 
stream which in its course forms many cascades. Between 
Hamakua and Hilo the traveler has to cross more than forty 
of these gulches, the largest of them, that of Hakalau, almost 
2000 ft. deep, while others do not exceed 100 ft. in depth. 
Hualalai, 8200 ft. high, has experienced several eruptions in 
the beginning of the present century, but none since. Probably 
it had formerly a pit-crater at its summit like Kilauea and 
Mokuaweoweo; at present the depression of its extensive summit 
is surrounded on three sides or more by a rim of moderate 
elevation, which recalls on a smaller scale the Circus of the Peak 
of Teneriffe without the central Pico de Teyde. In place of this 
both the bottom of the small caldera and its rim are studded 
by a multitude of small cones; some with a truncate top at once 
recognizable as tufa cones, others pointed and giving vent at the 
sharp top to a narrow chimney, often of unfathomable depth, 
so that the reverberation of a stone strown down will be heard for 
a quarter of a minute. The lava at the bottom of the caldera 
is concealed by a very porous and light scoria covering, through 
which the foot breaks at every step. 
Finally, Mauna Loa, the only active volcano at the present 
time, with its two ereat pit-craters, Kilauea and Mokuaweoweo, 
concludes the series of Hawaiian formations. With a base of 
nearly 60 miles from west to east and a height of 13,675 ft. it 
has a uniform and gentle slope of 5°, unbroken on all sides and 
bare of vegetation in its upper half, which is entirely covered 
by recent lava streams. No ravine or gully breaks the uniformity 
of its mantle, although the lower half is covered by dense forest 
— only here and there broken by recent lava streams — which 
causes large precipitation of rain, not only on the windward side, 
but, owing to a deflection of the trade-winds at the southwest 
end, also in the middle zone on the lee side. All the rain which 
falls, the annual average at Hilo being 180 inches, is absorbed 
by the porous rock and runs underground, to well forth in springs 
along the shore or farther out under the sea. 
The area between the three mountains, Mauna Kea, Mauna 
Loa, and Hualalai, is a triangular plateau of 5000 to 6000 ft. 
elevation above the sea, covered by broken lava and a stunted 
scrub vegetation. 
We have thus the following groups of formation: 1. Mauna 
Loa; 2. Hualalai; 3. Haleakala; 4. Mauna Kea; 5. Kohala range 
and West Maui; 6. Molokai and main range of Oahu; 7. Kaala 
range of Oahu, and Kauai. 
