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Range; east of Mount Lay, the stratigraphic range is at least 5,500 feet. Tt seems to form mainly from the decomposition of the remaining chlorite in the rock, though it probably also draws material from magnetite, and possibly from biotite. The garnets from the lowest grade metamorphic zone are irregular in outline and are pseudomorphous after patches or groups of grains of chlorite. Most of them enclose grains of quartz, biotite, and feldspar, commonly to such an extent that as much as 90 per cent of a large skeletal crystal may consist of inclusions. All stages of growth toward euhedral, dodecahedral crystals relatively free from inclu- sions can be observed in specimens of successively higher metamorphic grade. That this growth of crystals was taking place at a time of crustal movement is shown by spiral lines of inclusions in garnet porphyroblasts from about the middle of the Tenakihi group section, indicating a rotation of the grain during growth, and that at least some deformation had already occurred at the time of crystal growth is shown by helecitic lines of inclu- sions that preserve and early, wavy, crumpled ‘schistosity’ in garnets in a rock now almost eompletely recrystallized to coarse, regular layers.

The clinozoisite-epidote-bearing rocks are apparently restricted to beds of distinctive chemical composition. It has been established (Turner, 1948) that clinozoisite may occur in rocks with or without plagioclase, if the amount of available lime exceeds the maximum that can enter into plagioclase under the existing temperature and shearing stress. In almost all the other rocks in the Tenakihi group plagioclase appears to be the only essential mineral containing lime.

Kyanite forms conspicuous porphyroblasts in beds about 2,500 feet below the top of the Tenakihi group section; it is plentiful over a strati- graphic range of at least 3,000 feet, and persists as a few sparsely distributed crystals almost to the zone of highest grade metamorphism. Thus, a large part of the group falls within the ‘kyanite zone’. Coincident with the most plentiful kyanite, porphyroblasts of staurolite are abundant; their statigraphic range appears to be limited to about 1,500 feet, and within this range staurolite is confined to certain beds, presumably those rich in ferrous iron. Thus no true ‘staurolite zone’ appears to exist; but staurolite occurs locally within the kyanite zone.

The main change at successively lower horizons within the kyanite zone is one of slightly increasing grain size and a tendency toward gneissic foliation. Within 5,000 feet of the lowest beds of the exposed section, in the Tenakihi Range, and in almost the stratigraphically lowest beds in the Chase Mountain and Mount Lay areas, small, needle-like crystals appear in the grains of biotite, muscovite, and quartz. These crystals have been tentatively identified as sillimanite; although they constitute less than 1 per cent of the rock in all thin sections examined, the temperature and pressure conditions appropriate for their formation appear to have been reached, and the lowermost exposed horizons in all main areas of the Tenakihi group rocks may be tentatively considered to have entered the ‘sillimanite zone’ . In the stratigraphically lowest rocks of each of these areas, the crystalloblastic texture is considerably more regular than in higher beds; the mutually poikilitic texture, in which large irregular grains of biotite contain inclusions of quartz and feldspar, and large irregular grains of quartz contain inclusions of biotite and feldspar, has given way to