Harris mountains, the presence of which was reported by McKay (1881) and verbally by Butement (See Ulrich 1890). It is possible that other small outcrops occur between Lake Harris and the Lower Routeburn and Caples Valleys, as peridotite pebbles were found in the Routeburn Valley (1425, 1443, 1452), but no evidence of the extension of the main fault-zone which the peridotites invade has yet been noted immediately south of the Hidden Falls Valley, and the stretch between this and the serpentines traced by Hutton (1937) southwards from the east branch of the Eglinton Valley deserves detailed study. A general account of the petrology of these rocks in the Red Hills region was given by Ulrich (op. cit.), and in much greater detail by Turner (1930). Marshall's (1906) account of these by the Cow Saddle is the only source of petrological information concerning those within the present area. The few rocks which were collected during the present exploration do not permit us to add much to this. Marshall showed that at the Saddle there lies on the east a wide mass of Iherzolite with vertically dipping bands of more or less serpentinised Iherzolite and of diorite. Immediately west of this is a thin band of pyroxenite, followed by one of gabbro, merging into diorite which abuts against the Te Anau rocks of the Bryneira Range. Our most massive specimen (4737) of peridotite from Fiery Peak, though probably part of Marshall's Iherzolite, contains but little diopside, and approaches more closely to the harzbergites. The enstatite has locally passed into talc or less often bastite, but there are very few veinlets of normal chrysotile serpentine. The spinellid mineral is a chromite-picotite, but in addition thereto are a few crystals and irregular grains of an opaque mineral with metallic lustre which is possibly awaruite. Pebbles of normal schistose chrysotile serpentine were obtained on the saddle in the Olivine Valley three miles further north-north-east (Locality 23), and again on the eastern slope of Mount Frenchman (Locality 9), where it is associated with a gabbro that is but little different from that at Cow Saddle. In Marshall's slide (E 4) of this the plagioclase is entirely decomposed and replaced by cloudy translucent saussurite. The subophitic diopside is either quite fresh and in regular intergrowth with pale brown amphibole, or is replaced by very finely flaky antigorite often fringed with pale green actinolite, which may extend with complete crystallographic continuity into the brown amphibole. A few grains of pyrites are present. Serpentines of various types derived from the ultrabasic rocks in and beyond the northern margin of our area have been collected by Mr. C. Yunge in the Gorge (Jerry), Durward, and Red Pyke-Rivers (1495–9, 2475–6), and these, with a score of specimens obtained by Dr. G. Moir from Red Hill, a mile north of the boundary of our region (1238, 1258–61, 1403–1417) described by Dr. Turner (1930, 1934), and others collected by Mr. R. F. Landreth, illustrate a variety of altered peridotites, serpentines, gabbros, and their peculiar associated vein-rocks.