HEAT. 



271 



great breadth of the crater ; but the exterior has lost its natural slopes by 

 denudation. In Fig. 235 the cone to the left shows the dip of the layers 

 of tufa inward toward the center of the crater and outward, down the outer 

 slopes. Driblets pile up the fantastic driblet-cone, which has no crater but 

 simply a hole for the projection of lava in small liquid masses, drops, drib- 



lets, or worm-like streamlets. 



234. 



235. 



Tufa-cones, Oabu. Fig. 234, a, the tufa-cone, Diamond Head, east of Honolulu, the exterior eroded; 

 b, c, other smaller cones; Fig. 235, Koko Head tufa-cones, east cape of Oahu, the one to the left cut through 

 by the sea, that to the right eroded inside as well as outside. D. 



Still another kind of cone, occasionally observed in Kilauea, is the debris- 

 cone, made at times in Halemaumau after a discharge out of the masses or 

 fragments that fall into the basin from its steep sides. (See Fig. 231.) 



236. 



237. 



Driblet-cone of Kilauea. D. '40. 



Driblet-cone. Brigham, '64. 



At an eruption, the discharged lava : (1) may flow down the mountain 

 in great streams from the crater at the summit; or (2) may escape to the 

 surface through breaks or fissures made by the eruptive forces in the moun- 

 tain's sides, and thence spread away in streams ; or (3) it may flow off 

 through fissures into underground cavities between the old lava streams of 

 the mountain, or it may only fill the opened fissures. Discharges from the 

 crater are probably the prevailing kind at the commencement of a volcano, 

 the lavas then pouring out copiously. But at the present time the outflows 

 are mostly or wholly from fissures, though often subterranean. 



