KoA) UvAul: 269 
In the Wailua Valley, similar examples of columnar fracture and 
curved columns occur in some of the layers which compose the walls ; 
but symmetrical columns are not common. Near the banks of the 
stream, up three-fourths of a mile from the sea, a layer is convex for 
a short distance, leaving a large cavern underneath with a concave 
roof. Itis evidently an instance of a layer bulged by vapours beneath, 
while cooling, such as are common on Hawaii. The rock was sub- 
columnar, the fractures following nearly the course of radii drawn 
from the centre of the sphere of curvature. 
Curved columns often occur in places where, at first, it seems dif_- 
cult to account for them by reference to the position of the cooling 
surfaces. ‘The middle or interior of a layer, which, in other parts, is 
vertically columnar, presents, at times, singular examples of contorted 
columns; the straight columns curve to the right or left for a short 
distance, and then gradually resume their original direction. In ex- 
planation, we remark, that over streams of cooling lava, steam-holes re- 
main for many months, and often continue for a year or more after the 
eruption has ceased, emitting hot air and vapours; and under such 
circumstances, the cooling of the interior must take place very un- 
equally ; curvatures of various forms might, therefore, be produced, 
and still derive their peculiarities from the position of the cooling 
surfaces, or, what 1s equivalent, the direction in which the heat is 
drawn off. 
A spherical structure is exhibited in the rocks on many parts of the 
island. On the descent to the valley of the Nawiliwili, not far from 
the eastern shores, and also ascending from it, there appeared to be a 
pavement of cobble-stones along the steep declivities. The stones 
were concretionary nodules of the basaltic rock, and were three to 
twelve inches in diameter. ‘They had been brought out in relief by 
the superficial decomposition of the rock, which gave it a dirt-brown 
colour, and assisted in the deception. The layers of the nodules were 
gradually peeling off, exposing a harder interior, which did not exhibit 
a concentric structure. 
The mountains of Kauai are intersected by numerous dikes, which 
may be seen in many of the valleys where the walls are too steep for 
continuous vegetation. In the Hanapepe, about six miles from the 
sea, or two miles from the place of descent, the wall, which is not less 
than one thousand feet high, is cut through from top to bottom, by a 
dike but four feet wide. It was inclined on the face of the bluff 60° 
to the southward, and had a west-southwest course, as nearly as could 
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