54 C. H. HITCHCOCK VOLCANIC PHENOMENA ON HAWAII 



since the adjacent older streams appeared to allow much loose earth to 

 accumulate on them. I found two small areas of an ancient discharge 

 which were not covered by the later basalts, and retained the original 

 dense forest. One is a mile in diameter, east of Pahoa post-office ; the other 

 is much smaller, near the eighteenth mile-post. Large ohias, tree ferns, 

 ropy vines, and various shrubs are as vigorous in these small outliers as 

 in the upper forest, while the interspaces exhibit chiefly " pahoehoe " 

 basalt of recent origin, devoid of vegetation. The natural conclusion is 

 that the forest originally covered all the Puna district, and that the lava 

 flowed down so plentifull}'' from Kilauea or Mauna Loathat most of the 

 region was covered and the trees destroyed. The soil of these two out- 

 lying patches and of the 3 miles of forest crossed by the road near Hilo 

 came from the disintegration of basalt. 



The soil derived from volcanic ash extends along the Volcano road 

 for 10 miles above Olaa village. Sections at the twent3^-first mile-post 

 show two beds, each 6 feet thick, separated by a black band of vegetable 

 humus, with roots, thus indicating two separate discharges, the second 

 appearing many years after the first — a period long enough to allow of 

 the growth of a forest before that too was overwhelmed. Because of the 

 great rainfall these beds have been converted into a red clay. Similar 

 duplex deposits appear at the twentj^-second and twenty-third mile- 

 posts. Above the twenty-fifth mile post the forest and ash both disap- 

 pear and the surface consists of pahoehoe, bare of vegetation. This ex- 

 tends to about a mile east of Kilauea, where the vigorous vegetation still 

 remains. No eff'ort was made to follow this stream of lava to its source, 

 nor to demonstrate its connection with the barren tract outside of the 

 forests extending toward Pahoa. The various facts stated will illustrate 

 the method that may be employed to determine the j)osition and suc- 

 cession of prehistoric lava flows on Hawaii. "Aa" streams of great an- 

 tiquity underlie the ashes in the Olaa forest, apparently originating from 

 Mauna Loa. Kilauea emitted ashes, stones, and lava bombs at a more 

 recent date. They have .been noticed extending a mile east of the vol- 

 cano, 4 miles southwest from the pit and toward Keauhau. They are 

 coarser than the ash, of greater extent, and of a darker color, and con- 

 tain pisolite. It is very common to the southwest. 



The older ash is first seen about 4 miles southwest of Kilauea, and 

 appears in occasional spots as far as the Halfway house. It then in- 

 creases in amount and importance. Midway between the Halfway house 

 and Pahala there is a terrace of it 1,800 feet in altitude. In this neigh- 

 borhood it distinctly underlies both " aa " and i)ahoehoe. At Pahala 

 it is very thick and dry. The Hawaiians formerly amused themselves 

 by jumping into these piles of dust as though it were a liquid. The 



