220 J. D. Dana — History of the Changes in Kilauea. 



jets before they reach their limit usually have become divided 

 into clots, instead of remaining a continuous stream. 



The fact that the throw in the projectile action of a crater is 

 usually vertical is well shown in some of the columnar driblet- 

 cones This is the case in that of fig. 1 below, in which 

 the column was elongated vertically, although a result of suc- 

 cessively descending drops. In the figure referred to, the place 

 of ejection was at the base of the vertical part, and it is proba- 

 ble that the force which determined the slight obliquity in the 

 throw required for so uniform a fall on one side of it, was that 

 of the prevailing wind. This vertical throw, — due to the fact 

 that the top of the bubble is the weak, and, therefore the ex- 

 ploding spot—makes the projectile action good for throwing 

 up, but not good for a destructive bombardment of a crater's 

 walls. 



Common observations would lead us to expect that in a low 

 state of the fires, when the large lake is for the most part 

 thinly crusted over, the point of greatest heat and action would 

 be toward the center ; instead of this it is usually at the margin, 

 and often in oven-like places partly under the cover of the 

 border rocks. The only explanation that now appears is this : 

 that along the border, the outside cold, or that of the atmos- 

 phere, is much less felt than over the central portion. 



One of the secondary results, over the floor of the crater, of 

 the projectile work is the making of the fantastic driblet cones, 

 formed often about blow-holes out of the descending clots 

 and drops, as already explained. The forms of two of these 

 cones are shown in the following figures : the first from my 



Driblet Cones. 



Expedition Geological Report (page 177) representing a foun- 

 tain-like structure about forty feet high made of lava-drops ; 

 the other from Mr. Brigham's Memoir (page 423), representing 

 " the Cathedral " as seen by him in 1864, and also earlier and 

 later by Mr. Coan (xxxiv, 88). 



Occasionally the particles of the projected lava are small and 

 descend in small showers of loose smooth-faced but variously 



