126 



LORD HOWE ISLAND. 



altitude of Sand Dunes. I traced it to a level of 200 feet, or more, above 

 the sea, which compares favourably with the height of the dunes along the 

 Cape Otway coast, where AVilkinson* ascertained them to attain 200 feet. 

 Similar dunes were observed by myself about Anderson's Inlet. 



Neither does the dip of the Coral-sand rock, where inclined, exceed that 

 of the known inclination at which blown sand rests. The mean of the dips 

 taken is 28°, whilst, from observations made by Mr. C. S. Wilkinson and 

 myself at Cape Otway, it was found that the faces of the dunes stood at from 

 30° to 35°. 



Having endeavoured to account for the accumulation of the Coral-sand 

 rock chiefly through the agency of the wind, it now becomes necessary to 

 offer some remarks on the apparent unconformity visible between different 

 portions of this deposit. I have to candidly confess that, without a further 

 and more detailed examination, I could not venture on any absolute 

 explanation. It is possible, of course, that after the accumulation of 

 the lower or inclined series (PI. VII), a partial change of level took place, 

 giving rise to the tilting of the beds, after which the up2)er or horizontal 

 series was brought together in a similar way to the former. One point, 

 however, is very clear, a submergence took place after the final accumulation 

 of the Coral-sand rock, as evinced by the fact that it now forms the fore 

 shore, and bottom of the Lagoon, and is itself in course of denudation. To 

 bring about the necessary physical change to effect this, a general sinking of 

 the island must have taken place, and it is probable that it is from this 

 period that the present fringing reef dates its origin. A significant 

 fact in support of this is the statement on White's map that the 

 entrances to the Lagoon were only one fathom deep at low water. Now, from 

 the most recent surveys, we find that the water in the two main or navigable 

 channels varies from three and a half to five in the North Entrance, and 

 from four to seven in the South Entrance. If White's soundings are to 

 be depended on it looks as if we were here in face of an historical depression ! 



To sum up, it may be briefly stated that a marked break occurs in the 

 Coral-sand rock series, but whether this is due to depression and re-clevation 

 or to the known peculiar physical changes which iEolian rocks undergo is 

 not at present clear ; that after its final accumulation depression un- 

 doubtedly did talte place, resulting in the present geological and physical 

 aspect of Lord Howe Island. 



To regard the Coral-sand rock as of sedimentary origin is requisite the 

 assumption of a series of changes, for which there is no evidence, including 

 a direct depression of some 200 feet. That no elevation has taken place 

 since the present physical aspect was assumed is, I think, apparent. On 

 some of the Pacific Islands patches and blocks of coral, more or less semi- 

 fossilized, are found at high altitudes, clearly proving that emergence had 

 taken place whilst the present configuration of those islands was in course 

 of formation. Such an instance was observed by Stutchbury, at Tahiti, 

 where on one of the higher mountains he observed a bed of semi-fossil 

 coral. J So far as observed, no facts of this nature have been revealed at 

 Lord Howe Ishind. It is possible that the severance between the latter and 

 New Zealand took place during the subsidence spolcen of by Dana^ 

 " between the New Hebrides and Australia, the reefs and islands mark out 

 another area of depression which may have been simultaneously in 

 progress."§ R. ETHEEIDG-E, Jra-E. 



* Report on the Geology of the Cape Otway District, loc. cit., p. 26. 



t Trans. R. Soc. Yict. 187G, xii, p. 3. ' J Darwin, Geol. Obs. Vole. Islands, p. 28. 



§ Dana, Corals and Coral Islands, loc. cit. p. 829. 



