270 HAWAIIAN ISLANDS. 
be judged. Cross fractures indicated an imperfectly columnar struc- 
ture ; and, in some places, the dike was faulted. ‘Two other dikes were 
seen near by, but, on account of the vegetation, they were traceable 
only for a short distance. Scarcely any effect of heat in the walls of 
the dike could be detected; there was a slight change of colour to 
brown, and the rock was a little more cellular. But much alteration is 
seldom seen, when the rock of the dike is similar to that it traverses. 
In the Wailua Valley, about a mile from the sea, several dikes 
intersect the high walls on the south side of the gorge. They are 
from three to six feet wide, and have a southeast and northwest direc- 
tion. Three of these follow a nearly parallel course, diverging a little 
above, and they are all inclined to the westward. They are occa- 
sionally faulted, a common characteristic of dikes intersecting other 
basaltic rocks, owing to the many fractures in basaltic evens aad their 
tendency to break irregularly. 
Other dikes were observed on the island, but nothing of special 
importance was distinguished in the distant view we had of them. 
b. Eastern Shore Ridge. 
The range along the eastern coast, either borders the sea or extends 
along within half a mile of it; and the shore plain between it and the 
mountains, is from two to three miles wide. It is not continuous, but 
forms several isolated ridges, among which, the thin crest called 
Hoary Head, is one of the most prominent. The range faces the 
interior with an abrupt front, and has an uneven serrated outline. 
The declivities were mostly enveloped in a dense wood, excepting at 
base, where the ridge was often quite vertical. Some spots to leeward 
about the higher summits were covered with grass. In a few places 
columnar recks were distinguished. Wailua River intersects one of 
the ridges about half a mile from the sea. Near this place, parallel 
layers were distinct to the very summit of each of the rugged peaks. 
The dip amounted to eight or ten degrees, and in direction was north- 
eastward, or nearly towards the sea. The same dip was observed 
in summits near Nawiliwili, a few miles south of Wailua. In the 
course of one hundred and fifty feet in height, there were ten layers 
of basaltic rock, the thickness of each varying from ten to thirty 
feet. 
Back of Anahola, on the northeast shore of the island, eight or nine 
