438 J. S. Emerson — Some Characteristics of Kau. 



But, finally, no better evidence as to the origin of this minute 

 sand can be produced than its appearance under the micro- 

 scope. Its mechanical features are sharp and broken as of 

 volcanic sand, wholly unlike the rounded and worn features of 

 beach sand. In short, the positive testimony of chemical analy- 

 sis and microscopic examination shows that the mineral portion 

 of this soil is volcanic sand, not the wash from any higher level 

 of decomposed rock. This necessitates the theory of explosive 

 eruptions on a scale of magnitude proportional to the extent of 

 territory covered, which would have been greater but for the 

 ocean which abruptly terminates it along the entire coast from 

 Punaluu to South Cape, and a precipice on the southwest, 

 beyond which all trace of this soil has been effectually covered 

 up by flows of lava. Further, three great centers of volcanic 

 activity, viz., Kilauea, Mokuaweoweo and the vicinity of Puu o 

 Keokeo to the northeast, north and west respectively of the 

 district in question, have covered extensive areas about them 

 with other formations, so that it is impossible to locate the 

 original limits of this unique formation in those directions. 

 At the same time, the evidence is very strong, if not conclusive, 

 that neither of these three volcanic centers was its source, 

 while every consideration points to the great crater-like area 

 below Puu Iki. 



This locality is so little known and so difficult of exploration 

 that we are unable to point out the exact location of the center 

 of explosion. The unstable character of the material ejected 

 would tend in a measure to cover up its source, which from the 

 nature of the case could not be as sharply defined as that of a 

 flow of aa or pahoehoe^ whose birthplace is marked with solid 

 rock. 



As to the time when these remarkable explosions occurred, 

 it may be observed that the only event of this character in 

 these islands, of which we have any definite information, took 

 place at Kilauea a little over one hundred years ago, as already 

 stated. From the fact that the old cock-pits near Puu o 

 Keokeo and the ancient road leading to them remain as they 

 must have been left by King Umi 350 years ago, it seems quite 

 evident that no explosive eruptions on a large scale have taken 

 place during that interval either from the summit crater of 

 Mauna Loa or from the great lateral rift which has been so 

 active in building up the immense ridge which marks its 

 southwest slope. The conclusion therefore is evident that the 

 eruption which produced the Kau dust under discussion was 

 earlier than the beginning of the sixteenth century. Though 

 we may not locate the time of these eruptions as definitely 

 as the place, yet the fact that they form the last of a long 



