50 ~ J.D. Dana on Denudation in the Pacific. 
circular alcoves or recesses, which extended to the distant sum- 
mits over head: more commonly, the walls were formed of a 
series of i columns of vast size, collected together like 
the clustered shafts of a Gothic structure, and terminating sev- 
eral hundred feet above, in low conical summits. Although the 
sides were erect or nearly so, there was a profuse decoration of 
vines and flowers, ferns, and pacipbery ; and where more inclined, 
forests covered densely the slo 
These peculiar ree eatores proceed from the wear of 
rills of waters, streaming down the bold sides of the gorge; they 
channel the surface, leaving ny intermediate parts prominent, 
The rock is uniformly stratified, and the layers consist of gray 
basalt or basaltic lava, alternating with basaltic conglomerate. 
Cascades were frequently met with; at one place, a dozen 
were playing around us at the same time, pouring down the high 
walls, appearing and disappearing, at intervals, amid the foliage, _ 
some in white foamy threads, and others in Bait strands im- 
perfectly concealing the black surface of rock b : 
A rough ramble of four miles brought us % the falls of the 
Hanapepe. The precipice, sweeping around with a curve, ab- 
ruptly closed the defile, and all farther progress was therefore 
intercepted. We were in an amphitheatre of surpassing > ee 
to which the long defile, with its Auted or Gothic walls, decorat 
with leaves and flowers and living cascades, seemed a fit hich 
or eutrance-way. ‘Ihe sides around were lofty, and the profuse 
vegetation was almost as varied in its tints of green as in its 
forms. On the left stood apart from the walls an inclined colum- 
nar peak or leaning tower, overhanging the valley. Its abrupt 
oT were bare, excepting some tufts of ferns and mosses, while 
dant mountains above, where the basaltic recks stood out in 
curved ascending columns on either side, as if about to meet in a 
Gothic arch, a stream leaped the precipice and fell in dripping 
foam to the depths below; where, ee its strength again, 
it went ou its shaded way down the gorge 
The mountains of Tahiti commence their slopes from the 
sea or a narrow sea-shore plain, and gradually rise on all sides 
towards the central peaks, the ridges of the north and west ter- 
minating in the towering comiaiae of Orohet.a and Aorai, while 
the eastern and southern, though reaching towards the pig 
peaks, are partly intercepted by the valley of Papenoo. Aorai 
seven thousand feet in height and Orohena not less than eight 
ag apa feet. 
commenced the ascent of Mount Aorai by the ridge on the 
west oie of the Matavai Valley, and, by the skillfulness of our 
guide, were generally, able to e the e levated parts of the ridge 
