PAUL: 297 
But distinct and regular columns are seldom met with. One locality 
in the Matavai Valley, often described by travellers, was visited by 
Dr. Pickering and J. P. Couthouy of the Expedition. The bluff is 
from two to three hundred feet in height, and is neatly columnar 
throughout; the columns are five to eight inches in diameter and 
without regular transverse joints. ‘They stand nearly perpendicular, 
except a short distance up the stream, where they curve round in 
the form of a large segment of a circle. Singular curvatures are 
occasionally seen in columns forming the interior of a bluff. In 
the face of a precipice about five hundred feet high in the Matavai 
Valley, where the columnar structure was displayed with considerable 
perfection, there were several 
places in which the columns con- 
verged to a point, as is shown 
in the figure, and then gradually 
assumed their former direction. 
The breadth occupied by one of 
these clusters of converging 
columns, I estimated at ten feet, 
but others were much larger. 
The columns themselves were from ten to twenty inches in diameter. 
This anomalous structure has been explained on page 269. 
Dikes of basalt are seen in different parts of the island; but the 
rocks are so seldom bare of soil, that we have not been able to deduce 
any important conclusions from our investigations. If we may judge 
from the observations made, we should say that they were far from 
numerous, compared with most volcanic regions. Under One Tree 
Mill, just west of Matavai, tufa is intersected by several dikes run- 
ning to the southward and eastward, and varying in width from one 
to six feet. The rock is mostly compact and tough; it has a grayish- 
black colour, and contains some chrysolite, with an occasional crystal 
of augite. In the hill there are several faults, which dislocate the 
dikes in many places. Other dikes were observed in the Papenoo 
and Punaavia Valleys, some of which were remarkable for their curva- 
tures, passing sometimes to a horizontal position, and then resuming 
an upright course. Scarcely any indication of heat is found in the 
walls of the dikes, a fact which we observe to be almost universal in 
the case of one basaltic rock intersecting another. The tufas are, 
however, much baked for a few inches. 
One fact worthy of note connected with the dikes is that they are 
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