only was observed, and the fold axes shown on this map are based on “top-bottom” beds. They are the minimum number of possible fold axes rather than the true number, which is likely to be greater. Only one fold axis was observed directly. In the middle sub-schists at Trent Gorge the limbs do not progressively flatten towards the axes but meet sharply. If this is true generally, the wide range in dip of the beds cannot be due to flattening of the limbs towards fold axes. More probably, it is due to folding of the fold axes.

The structure of the Alps is known to be similar for many miles to the north and south of the area examined, and it can be reasonably assumed that the structure exposed at the ground surface does not differ appreciably from that at a depth of a few miles. The beds in this area vary in dip and in direction of stratigraphic top, and similar variations are likely in all cross-sections at right angles to the strike. All the observations have been projected on to a single line of section from Bell Hill through the Trent River Gorge to a mile east of Harper Pass.

From the western edge of the upper sub-schists to the conglomerates at the lower end of the Trent Gorge the dip is vertical and the strike regular. Top is to the east. Therefore this section is the west flank of a syncline, and the conglomerate is many thousands of feet stratigraphically higher than the Monotis beds at Mt. Monotis. At Confirmation Rill, on the east side of Trent River, top is to the west and the beds form the east flank of the syncline. But the dip, both at this place and at other places on the steep side of the Trent Valley below the main divide is east at 45°. This 45° dip is inconsistent with the range of dips adopted for the axial plane of the folds, and may be due to surface creep caused by the steep slope. If the synclinal axis is correctly placed, and if the sequence is not interrupted by important faults, the two Monotis localities cannot be at the same stratigraphic horizon. As the simplest interpretation of the cross-section, the volcanics at Monotis Gulch have been tentatively correlated with those at Confirmation Rill. The evidence for the position of the easternmost anticline is indirect. As far as is known, metamorphism does not appreciably increase or decrease east of Trent River. If this is correct, the beds are unlikely to increase or decrease appreciably in age, and the next anticline (or fault) cannot be far east of the Trent Syncline.

The section through the middle sub-schists is based on the Trent Gorge section (fig. 4); extra complexity is probable, but a more simple interpretation unlikely. The section through the lower sub-schists and the schists is diagrammatic. In this area it is tempting to assume that the folds progressively become more intense and more closely spaced in the direction of increasing metamorphism, and that the fold axes continue west with the same dip and pass into schistosity planes. But this interpretation meets with difficulties when the schist belt as a whole is considered. At Trent River and at other places on the east side of the schist belt the fold axes in the sub-schists appear to dip steeply beneath the schist belt. On the west side of the schist belt in Nelson and North-West Otago the fold axes in the sub-schists also appear to dip steeply beneath the schist belt. If a cross-section sketch is made across the full width of the schist belt it will be seen that it is difficult to postulate gently dipping fold axes in the central part of the schist belt where the schistosity planes are gently dipping. The relation of the fold axes to the schistosity planes is an important problem. It could perhaps be solved if cleavage planes and fold axes could be traced through to the lower sub-schists, a distance in the Trent River area of only three miles. But this will