Page:Popular Science Monthly Volume 67.djvu/685

Rh gallon is less than sixty. At Molokai, where the salinity is greater, it is stated that the cane is not affected unless the number of grains per gallon exceeds one hundred.

From all the facts available, the conclusion seems warranted that the underground waters descend to the seas from the highlands and remain free from admixture till the pressure of the ocean exceeds that of the descending stream, when a commingling of the two liquids results. When the ocean pressure becomes greater, because of excessive pumping, the brine will increase in amount. In a small island the ocean water will force itself inland quite conspicuously. Molokai illustrates this proposition. Our information is derived from a report of Waldemar Lindgren in the Water Supply and Irrigation Papers No. 77. The springs there are of three classes, of which only the first calls for consideration here, (1) those very near the shore, (2) those breaking forth up to the height of 2,000 feet, (3) running streams still higher.

Shallow wells near the shore show the following degrees of salinity or number of grains per gallon, 238, 403, 150, 126, 109, 86, 102, 86; of deeper wells the first gave 86 grains at the surface and became ocean water at 50 feet. The second became ocean water at 125 feet. At Naiwa there are 90 grains of salinity at 70 feet. At Kalamaula several deep wells gave 102 and 101 grains and pure ocean water. The American Sugar Company sank several deep wells at Kaunakakai, of which the first five had 150 grains per gallon; others ranged from 270 to 4-85 grains. The Risdon wells yielded 70 to 79 grains per gallon. Better results appeared in nine wells sunk at Kawela, many of them showing less than 50 grains of salinity. The fresh water is contaminated up to four or five feet above the sea level. None of the underground streams can be more than eight miles in length, and many do not exceed three. It is also probable that no impervious layer protects the underground water as in Oahu.

6. There are springs of fresh water near the sea-shore in Oahu which may correspond to the artesian fountains. One is the famous Kamehameha Bath near Punahou, a second is near the railroad station at Honolulu, and a third gladdens the thirsty soul at Waialua near the Haleiwa Hotel. Another is at Niu, west of Koko Head. It would seem that the underground water finds it way to the surface through some crevice, after the usual manner of springs, and that it is powerful enough to prevent the commingling of the ocean water with it.

The theory of the subterranean stream from the summits to sea level has been further tested practically by the driving of tunnels to reach the water near its source. Thus derived the water is free from any possible saline contamination, and being delivered by means of a ditch sloping downwards, the expense of sinking artesian wells and the subsequent pumping is saved. In this way a copious daily flow has