The series of beds containing graptolites in New Zealand occur in the Whakamarama district, which is situated in almost the extreme north-west of the South Island. They consist of intercalated bands of quartzite and carbonaceous argillites, with a north and south strike and dipping at a low angle to the west. As a result of the natural erosion of the land surface taking place more rapidly in the slaty layers than in the harder quartzites, the ridges and stream valleys exhibit a noticeable parallelism, those streams which enter the sea on the western coast usually taking a very sharp bend to the west, and with a somewhat gorgy channel to the sea. The valleys are for the most part densely clothed with forest trees, while the ridges of quartzite are barren, with the exception of a stunted growth of manuka (Leptospermum scoparium and L. ericoides), and in places a covering of peat to a depth of a few inches.