On the Limestones and other Rocks of the Rimutaka and Tararua Mountains.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 21, 1888, Page 486

Papers.—1. “On the Limestones and other Rocks of the Rimutaka and Tararua Mountains,” by A. McKay, F.G.S. Abstract. Mr. McKay said that several years ago Mr. J. C. Crawford endeavoured to draw attention to the existence of valuable building-stones in the immediate vicinity of Wellington; and he believed that Mr. Crawford partly opened up a quarry on his property forming the Miramar Peninsula. Attention was at the same time drawn to some rocks on the range north-west of the Botanic Gardens, which were subsequently examined by Mr. Cox, late Assistant Geologist. All of these rocks proved too hard to dress easily, and they had consequently not come into general use. In the month of October last, the speaker said, samples of a comparatively soft sandstone were brought to the Colonial Museum from the western slopes of the Tararua Mountains. Shortly afterwards he examined the rocks of the range forming the water-parting between the Ruamahanga and Manawatu basins, with special reference to the occurrence of limestone five miles south of Eketahuna, and close to the main line of road to Masterton. These limestones formed a bed 10ft. to 12ft. thick, and were sufficiently hard to take a good polish. They varied in colours, being red, green, or grey, and were usually veined with white calc-spar veins; but, unfortunately, at the outcrop, and apparently throughout, the stone was so much jointed that no blocks more than 2ft. 6in. appeared likely to be obtained. Later in the season, Mr. McKay said, he explored the eastern slopes of the Tararua Ranges between the Waingawa and Tauherenikau Valleys, and along the gorge of the Waiohine River. A great part of the high vertical walls of rock forming the Waiohine Gorge was formed of calcareous diabasic ash. The rocks appeared to be an altered volcanic ash, and would be very beautiful if cut and polished. In some parts of the Waiohine Gorge the more cal-

careous rocks of a mixed white and green colour would quarry in large blocks, and take excellent polish. They were, however, so situate that at the present time they could hardly be worked with profit. The line of calcareous rocks crossed the Tauherenikau and stretched along the Rimutaka Range to the railway-line at the foot of the steep incline on the west side of the “Summit,” but he could not say how far it was traceable as a calcareous band following the range south. On the western side of the range limestones of like character occurred, and amongst the specimens on the table was one obtained from the Otaki Valley, and presented by Mr. Wallace. The distance of the outcrop was about nine miles from the railway-line. The existence of calcareous rocks in the Makara Valley had been known for some time, on Mr. Thomas Robinson's land. Further to the north-west, in the adjoining property, there was a body of rock forming a thick bed, of which about 50 per cent. is carbonate of lime. This, too, appeared to have been of volcanic or tufaceous rock. He had obtained samples, but they had proved excessively hard. If this stratum had been softer it might have proved valuable stone, as it was capable of being quarried in blocks of any size up to 7ft. in length and breadth. The stone was capable of receiving a very high polish, and the more beautiful parts of the stratum might pay for working despite the drawback of hardness. On the sea-coast, at Red Point, about a mile to the east of Sinclair Head, some very beautiful specimens of red and green slates had been obtained. The red slates were overlain by a considerable amount of grey and reddish quartzite, the bands being curiously contorted, and the quartzite was overlain by some 25ft. to 30ft. of a hard, brown, jasperoid rock, veined yellow and white, which, though very hard, was very beautiful when polished. Over this last was a mixture of serpentine, hæmatite, and granular limestone or calc-spar, which was not too hard to cut and polish; and, as the sample before the meeting would show, it was a very beautiful rock. The total thickness of these rocks, including the quartzite, was about 300ft., and they were so situate and exposed that they could be quarried with comparative freedom, and at small expense. Were the means of transit to Wellington other than over a heavy and rugged beach to the mouth of Happy Valley, Mr. McKay said that there could be little doubt but that the red and green slate might be worked and placed upon the market at once; but, however beautiful the jasper rock might be, to work it would require the use of expensive machinery. Mr. Brandon considered the discovery of this marble most important, and he hoped it would prove a profitable industry for Wellington. It was a pity the rock was so hard; but, no doubt, with improved machinery this could be overcome. Judging from the samples on the table, if the stone could be procured at a reasonable cost, we could compete against the world in producing mantelpieces, &c. Mr. Park would like to know if the slates were quite oxidized and anhydrous. He pointed out that if this was the case the discovery would prove of great value to Wellington, where building-stones were much wanted. Mr. Robinson said that the specimens of marble referred to, from Makara, were obtained from the surface, where they had been long exposed to the atmosphere: the rock under the surface would probably not be so hard. Mr. McKay, in reply, said that the rocks were composed of material completely oxidized, and that in the quarry this was shown by the absence of stains along the joints. He quoted the analysis, which showed that the rocks only contained a little more than 1 per cent, of water. He also read extracts showing that some of the marbles closely resembled the mixed characters of the verde antico of the Italians, and the African breccia marbles.