Crossing the Wailua River is a ridge several hundred feet high less than a mile back from the shore, rising abruptly above the plain. This would naturally represent one of the older lavas. Back of Anahola a similar wall is pointed out, where a hole has been worn through the hill.
Professor Dana suggests the possibility of tire presence of a second principal dome to account for the greater elevation of the land in Napali on the shore opposite to Niihau. The two islands have cliffs in a line with each other. If we could imagine some volcanic disturbance of a late date that should fracture the ledges, we could readily understand how the debris should have disap peared later by the action of the waves. Granting the presence of a dome between the islands the structure would simulate that of Oahu and Maui where two eruptive mountains have been con nected by necks of later-formed material.
In Koloa there are several secondary volcanic cones in an area of eight or ten square miles. The lavas are black with the pecu liar ropy structure and beneath are caverns, either the result of bulging or left by the streams that were protected by the con gealed surface. Unlike those back of Hilo, they do not show any stalactites; but being near the sea the waves of the ocean press into the cavities and spout from orifices quite high into the air. In this neighborhood are the celebrated barking sands, as well as at Mana at the extreme western end of the island. Some of the soils are intensely red in color because the growth of the vegeta tion brings the iron into new combinations with organic acids.
The shores of Kauai are lined with coral reefs and limestones, which are disintegrated and washed into beaches, and may be blown inland considerable distances. Some of these wind-driven sands reach altitudes of thirty-five and fifty feet and become con solidated. It is difficult to draw the line between the wind-blown sands and beaches formed by elevation of the land, both of which undoubtedly are to be found here as on Oahu.
A confirmation of our belief in the greater antiquity of Kauai over the other islands is derived from the study of the plants. This is presented forcibly by Dr. William Hillebrand in his Flora of the Hawaiian Islands. Taking the extremes, it may be stated that the flora of Mauna Loa is the poorest and most uniform, and that of Kauai the richest and most individualized in species. On
the whole the intervening islands follow the same ratio when al lowance is made for differences and elevation.
"The monotony of the forests of Puna, Kau and South Kona on Hawaii, will strike every attentive visitor and disappoint the botanical collector by the scarcity of the harvest. This can hardly he ascribed to the periodical destruction of forests by lava streams, for these follow with long intermission, affect only limited areas at a time, descend mostly down the northeast slope, and it is sur prising to see how quickly the ruin is repaired, how speedily de composition takes place in the lava when exposed to the influence of copious rains and the trade winds. In 1862 I visited the lower end of the lava stream which in 1856 had cut its way through the forests toward Hilo. A belt of thirty feet in width on each side of it was covered with a shrubby vegetation which had already attained a height of three to four feet. In the break of the pall of Oahu at the head of Nuuanu valley, through which the trade winds sweep with intense force nearly the entire year, one could observe hard compact basalt gradually softening until it could be cut with a pocket knife. And with how little soil plants are con tent when favored by copious rains is exemplified by the fact that the natives of Puna, Hawaii, raise good crops of sweet potatoes in the hollows and cracks of bare lava by simply covering the bud ding sprigs with decayed leaves and herbs. In the same region I once saw a cocoanut lying on smooth pahoehoe lava which had germinated there and sent off a root for a distance of eight inches until it met a crack down which it descended. On the other hand, the same kind of lava when not affected by rain and wind will re main unchanged for centuries, as may be seen under the lee of East Maui. Nowhere else have the forests, although extensive, so gregarious a character as within the area of Mauna Loa, and the species which comprise them show hardly any variation from those forms which are met with more to the east. The forests of Hilo and Hamakua, which belong to the region of Mauna Kea, are already more diversified, and still more those of the Kohala range.