112 



LORD HOWE ISLAND. 



the extreme, but the interior topography is simply useless. The coast and sea 

 details are, however, given with great exactness. The third map with which 

 I am acquainted, was published in connection with the Hon. J. Bowie 

 "Wilson's Eeport on Lord Howe Island in 1882. This, entitled "Lord 

 Howe Island and adjacent Islets and Reefs," is on a scale of three and a 

 quarter nautical miles to one inch, seems to be an improved edition of 

 the former map as to the execution, with much greater topographical 

 detail. In one particular, however, the two charts do not agree, the heights 

 of the principal elevations. The greatest discrepancy exists between that of 

 Intermediate Hill. In the " Herald " and " Torch " chart the height of this 

 is given as 841 feet, but in the 1882 map as 647 feet, a difference of 194 

 feet. The latter map was used by Mr. H. T. Wilkinson as the basis of 

 the geological map accompanying his Geological Eeport on Lord Howe 

 Island in 1882 (PL X). 



II. — Geology. 



The general geology of Lord Howe Island is extremely simple, but the 

 details are more complicated. The island consists practically of two forma- 

 tions only — the volcanic rocks forming the general mass, and the stratified 

 beds resting on them. The time at my disposal, through numerous other 

 duties claiming attention, rendered a study of the whole in detail an 

 impossibility, and such a proceeding, indeed, did not come within the scope 

 of my instructions. An examination of the volcanic rocks sufficiently to 

 permit the writing of a memoir on them would occupy much time, and 

 could not safely be performed by one observer. I was not even able to 

 solve many problems connected with the stratified deposits, and other very 

 important points must still remain open, a settlement of which would have 

 materially assisted the conclusions attempted to be drawn from the geology, 

 so far as known to me. 



1. Volcanic Series. — Two thirds of the island is composed of volcanic 

 rocks, comprising the three isolated masses already mentioned. The only 

 sections visible from the densely wooded nature of the ground, and rounded 

 outline of the eminences, are along the coast, and on the precipitous sides 

 of Mounts Grower and Ledgbird. As seen from the water, the exposed volcanic 

 rocks present a stratified structure, having the appearance of those of sedi- 

 mentary origin, " but a close inspection shows them to be made up of 

 different horizontal beds of volcanic rock."* In no place is this more 

 apparent than on the westerly faces of Mounts Grower and Ledgbird. An 

 excellent section may be examined by ascending the steep foot of the latter, 

 from the beach, for 300 feet or thereabouts, to the " Lower Eoad," which 

 runs for a portion of its more accessible course, more or less horizontally 

 parallel with a magnificent exposure of volcanic agglomerate, which is overlain 

 by a vesicular basalt, and this in its turn by an apparently harder stratum 

 of closer texture. So far as measurements with the eye alone can be relied 

 on, these beds appear to be from 15 to 30 feet thick. A somewhat similar 

 succession is again seen at the "Black Eocks," at the west sea-foot of 

 Mount Ledgbird, where a very fine agglomerate is followed by a vesicular 

 basaltic rock. In no part of the island is this stratification seen to better 

 advantage than along the sea face of the North Eidge, as viewed from the 

 water below. There a section, 700 feet high, can be scanned at a glance, 

 showing what certainly appears to be a successive alteration of beds of 



* H. T. Wilkinson, Geological Eeport, loc. cit., p. 4. 



