Transactions and Proceedings of the New Zealand Institute 1902 [electronic resource]

Volume 35, 1902

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Art. XXXIII.—On the Marine Mollusca of Totaranui Bay, Nelson.

By Professor james park F.G.S., Director, Otago University School of Mines.

[Read before the Otago Institute, 13th May, 1902.]

Totaranui is situated on the shores of Tasman Gulf, some forty miles north-west of Nelson, and about midway between that place and Collingwood. A crescent-shaped beach of golden sand-nearly a mile long and terminating at the ends against bold headlands of granite crowned with dark evergreen forest, a low terrace and shallow lagoon behind the beach, undulating fern-clad foot-hills beyond the flat, and a background of high forest-covered ranges, form, with a perfect climate, one of the most charming and picturesque spots in a region famed for the beauty of its summer retreats.

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The beach is steep, except at the north end, and composed of very coarse quartz sand and broken shells. It is sheltered from all winds except from the north-east, east, and southeast.

Excluding the recent alluvia forming the flat around the lagoon, only one rock-formation is represented in this district—namely, a crumbling grey-coloured granite, which is generally extremely coarse in texture. The feldspars of this granite exist mostly in large tabular crystals commonly from ½ in. to 1 in. long, but often reaching a length of 3 in. or more. The quartz is the predominant constituent. It occurs in large grains and irregular aggregates, which become prominent on all weathered and water-worn surfaces, thereby imparting a rough and rugged appearance to all the rocky headlands facing the sea. In such a coarse-grained rock the mica occupies a very subordinate place, and, in most parts is hardly perceptible to the eye.

On the coast-line between Totaranui and Anapai going north, and between Totaranui and Awaroa going south, the granite is traversed with veins of grey-coloured crypto-crystalline quartz, varying from a mere thread to 3 in. or 4in. in thickness. A mile before the Awaroa River is reached the grey granite is displaced by a wide belt of pink or reddish-coloured granite of intense hardness, and admirably adapted for a building-stone. This belt of pink granite is more than 100 yards wide, and in the direction of Awaroa is followed by the grey granite, which thence stretches southward for many miles without interruption.

This granite is a rock of great antiquity. At Takaka and Riwaka it is seen to be associated with crystalline limestones and quartzites of Lower Silurian age, and the geological considerations detailed in my report on the geology of Collingwood County^* afford good reason for the belief that the rocks in this and the surrounding region are the most ancient in New Zealand.

During a three-months residence at this beautiful place in the summer of 1901-1902 the writer collected 149 different species of Mollusca, including only those whose soft parts are protected with a shell or hard covering. This comparative poverty in molluscous life is doubtless due in part to the extremely coarse and ever-shifting sands, the absence of beach muds and fine sediments, and the exposed position of the enclosing rocky headlands.

On the other hand, it must not be forgotten that Totaranui is but a small nook in the great gulf contained between Cape Farewell Spit and D'Urville Island, and it is certain that a

[Footnote] * Geol. Rept. and Explorations, 1888-89.

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search of the adjoining bays, which in many instances present a great variety of conditions, would discover a much larger assemblage of marine shells than that enumerated in this paper.

In this collection the Brachiopoda are represented by three species—namely, Terebratella rubicunda (rare), Magas evansi (rare), and Rhynchonella nigricans (very rare). Of the latter only one example was found.

Among the fifty-two Conchifers the most common genera are Mytilus, Chione, Venus, Tapes, Vola, Mactra, Mesodesma, and Pecten.

The Polyplacophora are singularly scarce, only two species being found—namely, Chiton quoyi and Ornithochiton undulatus—and examples of these are by no means common.

The most prominent genera of Gasteropoda are Patella, Haliotis, Turbo, Diloma, Ancillaria, Natica, Trophon, Murex, Struthiolaria, Turritella, and Amphibola.

The Cephalopoda have only one representative—namely, Spirula pironii.

It may be noted in passing that the Echinodermata were observed to be represented by four species—namely, Evechinus chloroticus, Arachnoides placenta, Echinocardium zealandicum, and Echinobrissus recens. On a few occasions, after heavy south-east weather, the latter was thrown on the shore in thousands, but, being so fragile, perfect specimens were not often found.