OAHU. 245 
sands of the seashore at the foot of the hill often consisted half of chry- 
solite. 
Salt Lake Region.—The salt lake of Oahu is one of its principal 
curiosities. It occupies a depression surrounded by a low ridge, and 
is situated about three-fourths of a mile from the sea, and eight miles 
west of Honolulu. It is not at first apparent that its site was once a 
region of hot water and tufa eruptions. Yet, from the character of 
the tufa, and the direction of its dip, such was the case. There were 
evidently several] vents of considerable lateral extent, but of small force, 
and they resulted in producing a plain a mile and a half in its longest 
or east-and-west diameter, bounded by the low ridge referred to. The 
general character of the region is shown in the annexed topographical 
sketch, which includes, besides the basins, part of the valley on 
the east. ‘T'wo circles united form the larger part of the plain, in 
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which the lake is situated ; but there are three or four others of smaller 
size farther to the west, in immediate connexion; and one to the 
northeast (b), which is quite deep, and regularly bowl-shape. The 
ridge on the south is but fifty feet high; while on the north (near @) 
it is two hundred feet. It consists of tufas similar to those described. 
Ascending the north side, or that away from the sea, we look down 
on still another flat plain, surrounded by a low ridge, which, on the 
north and west, is but forty feet high. In its western corner (c) there 
is a deep bowl-like crater, with a high circular wall of stratified tufa. 
In structure and composition, the walls resemble those of the other 
tufa cones. The following view, taken from the harbour of Honolulu, 
62 
