OAHU. 241 
features of the mountain range, with its valleys and ridges. The top 
is also broken into miniature peaks, which are highest on the southern 
side. In consequence of this degradation of the sides, the stratifica- 
tion is distinctly seen far at sea. In the first distant view the lines 
appear to indicate different streams of lava, but on closer inspection 
they prove to arise from layers of tufa. The tufa is very friable, 
yielding easily to the fingers. It consists of thin lamine, as distinct 
as many alluvial deposits, and often separable. The layers vary in 
texture from a fine earth to a bed of pebbles, and have a brownish 
colour. They are often incrusted by a chalky coating of carbonate 
of lime, or are interlaminated with thin calcareous seams or plates.* 
The extent of degradation over the sides of Diamond Hill is very 
apparent in the fact that the layers constituting it present exposed 
edges on nearly every side of the cone. It is on this account a less 
satisfactory place for ascertaining the dip of the tufa than at some 
others of the tufa cones. Where best exhibited the angle appeared to 
be about thirty degrees. But the dip of the exterior and interior are 
in a reverse direction, the latter sloping towards the centre, instead of 
outward. The rim of the crater is in the dividing plain between the 
opposite slopes of the layers. In appearance there is an anticlinal 
axis; but it is obvious that the ejected earth and cinders, as it formed 
arising barrier around the opened vent, would fall on two declivities,— 
the zaner or that within the crater, and the outer or exterior of the 
cone. The layers resulting would have this double slope, as is ex- 
emplified by most tufa cones. 
Although no lavas can be traced from this crater, large streams lie 
near its eastern foot. Between Diamond Hill and the mountains, a 
distance of a mile, there is a slight elevation of the country, and about 
half way there are remains of a crater; yet it is so low as to be barely 
traceable in a distant view, and is only a hundred feet above the 
sea. The crater is nearly circular, about three hundred yards in 
diameter, and fifty feet deep. This vent appears to have been the 
source of the lavas alluded to that now cover the plain near Diamond 
* A somewhat similar occurrence of lime at the Cape Verdes, is mentioned by Mr. Dar- 
win in his Volcanic Islands, p. 13. 
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