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



no such beds of tufa or conglomerate, and no tufa or sand beds 

 of any kind intervening between the beds of lava constituting 

 them. There are fresh-looking lava-streams over the slopes of 

 Kilauea southwest of the crater, but none appeared along the 

 route to Punaluu of more recent date than the cinder deposit. 



15. The aa lava streams. — The aa areas, looking like 

 ploughed-up lava streams on a majestic scale, occur in the 

 course of outflows of both Kilauea and Mount Loa, and a small 

 area of the kind now exists (see map) in the floor of Kilauea. 

 Several of them were seen on the way up from Keauhou to 

 Kilauea ; one about ten miles from Kilauea in Kapapala, near 

 the road to Punaluu, three near Punaluu on the southern 

 border of Hawaii, and one on the lava stream of 1881, within 

 six miles of Hilo. The coarsest and most characteristic of 

 them are those near Punaluu ; and that near Hilo has special 

 interest. In crossing Hawaii in 1840 I was over others be- 

 tween Punaluu and Kaulanamauna. My new study of them 

 has led me to a change of opinion as to their mode of origin 

 and to an explanation not yet on record. The description 

 which follows will give others an opportunity to speculate 

 about them. 



An aa or arate lava stream consists of detached masses of 

 lava, as far as is visible from the outside. The masses are of 



very irregular shapes, and confusedly piled up to nearly a com- 

 mon level, although covering often areas many miles long and 

 half a mile to a mile or more wide. The size of the masses in 

 the coarser kind varies from a few inches across to several yards. 

 The Irock constituting the body of the mass is the ordinary 

 solid* lava, usually little vesiculated, not the scoriaceous ; but 

 the exterior surface is roughly cavernous and horridly jagged, 

 with projections often a foot or more long that are bristled all 

 over~with points and angles. In some cases ragged spaces ex- 



