GEOLOGY. 



113 



agglomerate, and a harder and denser rock, seamed in all directions by 

 dykes and veins, a number of which are quite vertical, and run up the face 

 of these magnificent clift's like so many ladders. 



The rock so frequently spoken of as an agglomerate consists of a reddish- 

 brown, or otherwise darker base, containing fragments of other volcanic 

 rocks from a few inches in diameter up to a hundredweight. Amongst the 

 best exposures of this rock I may mention the headland immediately to the 

 north of Ned's Beach, and between the Clear Place and Observatory Point 

 on the eastern side of the island. At the former place many of the con- 

 tamed blocks are of an immense size, and, from weathering lighter than the 

 base, give to the whole a remarkable appearance. This agglomerate rests 

 upon a vesicular and somewhat scoriaceous rock full of smalf crystals. 



At the latter locality the agglomerate forms a rugged and dangerous 

 beach, and is here again associated with a scoriaceous basaltic rock and is 

 much traversed by dykes, having a general north-easterly and south-westerly 

 direction. A dense dark greenish-brown basalt also occurs here, but time did 

 not permit me to satisfy myself of its relation to the general series, but it 

 seemed to be an interbedded rock. 



This basalt was said to contain tin, and about thirty tons were illegally 

 removed some years since to Auckland, IST.Z. It was reported to have 

 yielded 40 per cent, of tin, but on an official assay of the material being 

 made m Sydney it was found to be quite destitute of the metal. As it was 

 still asserted on the island to be stanniferous I brought tvpical samples 

 away with me, but on treatment in the Geological Survey "Laboratorv by 

 Mr. J. H. Mmgaye, they were again found to beVorthless.* 



This rock has been petrographically examined by Mr. T. W. Edgeworth 

 David, of the G-eological Survey Branch, who finds it to consist of a^-ound 

 mass of triclinic felspar, granular augite, and dendritic aagregations of 

 magnetic iron, and grains of olivine. 



On the east coast of Pobbin's Point occurs a light blue or greenish gray 

 basalt, also apparently an interbedded deposit. It contains veins and 

 scattered crystals of iron pyrites, and, according to Mr. T. ^Y. Edgeworth 

 David, IS a hard dense diabasic basalt. He believes it to be one of the 

 oldest rocks on the Island. Mr. H. T. Wilkinson states that a somewhat 

 similar rock is mot with on the east coast of Boathaven. The pyrites from 

 this locality yielded 3 dwt. 14 gr. gold, and 3 dwt. of silver to the ton. 

 Samples brought from Eobbins' Point by myself did not yield cither of the 

 metals on assay by Mr. Mingave. 



In a small bay, intermediate" between Wilkinson's Promotory and Middle 

 Beach I observed a beautiful exposure of a brick-red volcanic deposit, very 

 mucli resembling an ash, and forming a moderately high cliff. It was 

 associated with an agglomerate, and traversed by dykes. 



The latter form a most important feature in the geology of Lord Howe, 

 and are well worth a study simply in themselves. They were observed 

 varying m width from 6 inches to as much as 18 feet, and many must even 

 be much wider. They are usually denser and finer in texture than the rocks 

 m which they immediately occur, and, as a rule, stand forth like walls, 

 usually weathering into square or oblong blocks, and presenting a somewhat 

 concretionary structure. Excellent examples may be examined at the 

 Black Eocks, at the west sea-foot of Mount Ledgbird ; and again the rocky 

 shore of the Lagoon between Boat Pool and North Bay is seamed with them, 



* For full particulars of tliis 

 Papers, I8S3, No. II. 



case and the parties concerned, see Legislative Assembly 



