(1) The District Extending two and a half miles West of Tawaki
When proceeding eastward along the north coast of Natewa Bay one enters the region of acid rocks between 2 and 2½ miles west of Tawaki. Here the country is much broken, picturesque hills with bare precipitous faces rising up near the coast, one of which named Natoto has a rudely conical and truncated form. Grey oligoclase-trachytes having a specific gravity of 2·4 and possessing the characters described on page [308], prevail in the district extending west of Tawaki. Sometimes they occur in mass; but they often form agglomerates. A singular pitchstone-agglomerate occurs at the coast at the foot of Natoto. The pitchstone, which has a specific gravity of 2·48, is a semi-vitreous form of a hypersthene-augite andesite. It shows abundant small pyroxene prisms in its glassy groundmass and is referred to the prismatic sub-order (5) described on page [289].