APPENDIX. 417 
from Rocky Hill) with 30 feet of “ clay” below it, intervenes between the 
first and second beds of coral limestone, which two have together a thickness 
of 170 feet. It is an interesting example of the adverse circumstances attend- 
ing coral growths about an island of active fires. 
The author is unable to find in the facts from these wells evidence that 
sustains, as urged by Mr. A. Agassiz,’ the Murray hypothesis, or anything 
that sets aside the various objections to this hypothesis that have been pre- 
sented. In two of the Oahu wells, the Jaeger well and one of the Govern- 
meut wells on the Waikiki road, according to Professor Alexander, carbonized 
cocoanut-wood was found at a depth of about 150 feet, beneath a 150-foot 
stratum of coral. ‘This and all the other observations in connection with the 
wells are fully explained by the theory of subsidence. 
Oahu is an example of an island that has had an upward shove, notwith- 
standing the progressing subsidence. The amount of elevation indicated by 
the elevated coral reef is about 25 feet on the south side and 50 to 60 feet on 
the north side. The Kahuku bluffs of the vicinity of the north cape are not 
made wholly of drift sand, as Mr. Agassiz concluded from his observations. 
The bluffs have a top layer of wind-drift origin, while the rest, 50 to 60 feet 
high above the sea-level by estimate, is true coral reef rock, as the author has 
illustrated elsewhere. Such a change of level, as already stated, is not 
against the subsidence theory ; it is one of the common incidents of a volcanic 
region.” 
Il. RATE OF GROWTH OF CORALS AND CORAL REEFS. 
Arrangements made at Tahiti for measuring the rate of growth of a coral 
reef. — The arrangements made by Captain Wilkes for measuring the rate 
of growth of coral reefs are mentioned on page 257. A memoir by MM. Le 
Clerc and De Benazé was published at Paris in 1872, giving an account of 
their attempts to make use of the stone planted by Captain Wilkes. They 
made various measurements; but they observe that Wilkes does not state 
1 Coral Reefs of the Hawaiian Islands, by Alexander Agassiz, Bulletin of the Mu- 
seum of Comparative Zoology, 1889, X VII., 121. 
2 The fact that corals were growing about Oahu during the time when tufa eruptions 
were in progress over the southern border of the island, is proved by facts recently com- 
municated (Dec. 11, 1889) to Professor Alexander, by Rey. 8. E. Bishop, of Honolulu. 
He observes that in Halawa, Ewa, at the cutting for the railway across two small bays of 
Pearl Lochs, and south of Kuahua Island, there occur, in the finely laminated tufa, layers 
of comminuted shells and corals. Mr. Bishop concludes that these materials were “ prob- 
ably torn off from the sides of the fissure of ejection that was presumably opened through 
the anciently subsided strata of corals and shells.” Fragments of corals and shells were 
still more abundant over the top of the tufa. Scattering pieces of coral were also observed 
by Mr. Bishop imbedded in the tufa of the low craters southwest of Koko Head. 
27 
