GEOLOGY AM) T01'( )( i H A IM I Y ( )F 1 1 A W A 1 1 127 



island in Pearl Ilarlxu" and fi'csh walt-r was secured at a deplli of 24(1 feet. 

 The uatui'al principle involved in I he fresh water S])i'inu' and esp(M'i;ill\- the 

 spring in the ocean, was tui-ned to practical account. To secure water, wells 

 v/ere driven deep enouuh into the earth to puncture the iiioi-e oi' less iiii|)er\ious 

 strata overlying the water-bearing strata beneath, with tlie result that owinu- to 

 the pressure or head on the enipounded water, it rose in the well, and in the 

 lowei' zone about the island often overflowed to form an artilicial spiini;- or 

 flowing artesian well. The principle involved in wells which do not ovei'tlow 

 is the same as that in those that do; for which reason all deep wells are now 

 called artesian. Wells in which the water is raised to the surface In- pumps are 

 liable to become brackish, through excessive ])umping, while those which flow- 

 naturally seldom show a marked change in the amount of salt carried in their 

 waters. 



The waterdiearing stratuin on Oahu at the sea-shore, is usually found to be 

 between three and four hundred feet below tide level, and is usually a very 

 porous basalt, capped wdth an overlaying impervious stratum usually of basalt. 

 Wells drilled in the vicinity of Honolulu at an elevation above forty-two feet 

 above the sea have to be pumped. The flowing wells are. as a rule, found at 

 the lower levels. It is of interest to note in this connection that as a rule the 

 shallowest wells are those bored about the ends of radiating lava i-idges and 

 that usually their depth increases the nearer they are to the sea-coast. Wells 

 drilled in the middle of valleys are usually deeper than those at either side. 

 All of these facts taken together indicate that the island has ])een submei-ged 

 to considerable depth before the subseciuent elevation of the raised coral reef 

 on the costal plain -AUmt the island, and that the reefs were laid down in sub- 

 merged valleys that wert' already dee[)ly eroded l)efore the reefs were formed 

 in them. 



In several places, notably at Waianae and Oahu plantations, as well as else- 

 where in the group, underground streams have been encountered through hori- 

 zontal tunnels driven into the mountains, and the underground v/ater sui)ply has 

 been tapped near its head. The tuiuiel is then extended to the right and left, form- 

 ing a Y-shaped drain, which brings the water to the surface, far aboxc possible 

 contamination with sea water. Such tuiniels are usually driven a1 altilude-, sufli- 

 cient to admit of distributing the watei- by gravity ovei- extensive fields well 

 upon the slopes of the mountain. On Maui a daily t1o'.\- of six million Lialhins 

 has IjCfcU secured in this wa\- at an elevation of 2,()0() feet. The woudei-ful Waia- 

 hole tuiuiel on Oahu. built on a modifiejition of this principle. deliver~> lwciit\- 

 million uallous of w-ater each t wenty-l'oui- lioui's. 



Economic PKonrcrs. 



Of the economic products, clays are the most important and are found on 

 Oahu, .Maui and Hawaii, in many jtlaces. in \aryiiig amoiuits. A number of 

 years ago a brick kiln was oi)ened in Nuiianu X'alley and brick of fair (piality 

 was manufactured. Unfortunately, the attempt was abandoiietl in. a short time. 



