532 
Prof. Liversidge — Chalk in New B ritain. 
rock debris” mentioned by tbe late talented David Forbes, F.R.S., 
probably consisted largely of silica. 
The only locality for chalk in the Pacific Islands to which I can find 
any reference occurs in Dana’s work on “ Corals and Coral Islands,” 
see p. 308. Put tbis even is not true chalk ; it is merely a recent 
limestone derived from disintegrated corals, and which resembles chalk. 
“The formation of chalk from coral is known to be exemplified at 
only one spot among the reefs of the Pacific. 
“ The coral mud often looks as if it might be a fit material for its 
production ; moreover, when simply dried, it has much the appearance 
of chalk, a fact pointed ont by Lieutenant Nelson in his memoir on the 
Eermudas (1834), and also by Mr. Darwin, and suggested to the author 
by the mud in the lagoon of Honden Island. Still this does not explain 
the origin of chalk, for, under all ordinary circumstances, this mud 
solidifies into compact limestone instead of chalk, a result which would 
be naturally expected. What condition then is necessary to vary the 
result, and set aside the ordinary process ? 
“ The only locality for chalk among the reefs of the Pacific, referred 
to above, was not found on any of the coral islands, but in the elevated 
reef of Oahu, near Honolulu, of which reef it forms a constituent 
part. It is twenty or thirty feet in extent, and cight or ten feet deep. 
“The rock could not be distinguished from much of the chalk of 
England ; it is equally fine and even in its texture, as earthy in its 
fracture, and so soft as to be used on the blackboard in the native 
schools. 
“ Some imbedded shells look precisely like chalk fossils. It con- 
tained, according to Professor Silliman, 92-80 per cent. of carbonate of 
lime, 2-38 of carbonate of magnesia, besides some alumina, oxide of 
iron, silica, etc. 
“ The locality is situated on the shores, quite above high-tide level, 
near the foot of Diamond Hill. This hill is an extinct tufa cone, 
nearly 700 feet in height, rising from the water’s edge, and in its 
origin it must have been partly submarine. It is one of the lateral 
cones of Eastern Oahti, and was thrown up at the time of an eruption 
through a fissure, the lava of which appears at the base. There was 
some coral on the shores when the eruption took place, as is evident 
from imbedded fragments in the tufa; but the reef containing the 
chalk appeared to have been subsequent in formation, and afforded no 
certain proof of any connexion between the fiies of the mountain and 
the formation of the chalk. 
“ The fine earthy texture of the material is evidence that the deposit 
was not a subaerial sea-shore accumulation, slhce only sandstones and 
conglomerates, with rare instances of more compact roeks, are thus 
forrned. Sand-rock making is the peculiar prerogative, the world over, 
of shores exposed to waves, or strong currents, either of marine or of 
fresh water. We should infer, therefore, that the accumulation was 
produced either in a confined area, into which the fine material from a 
beach may have been washed, or on the shore of a shallow quiet sea — 
in other words, under the same conditions nearly as are required to 
produce the calcareous mud of the coral island. But, although the 
agency of fire in the result cannot be proved, it is by no means im- 
