of these authors will be discussed in so far as they apply to the Wellington area. Miller's comment (p. 89) that the criteria are of varying value is still true; a single criterion may be conclusive evidence of faulting, another may be of little value by itself.

1. Fault fractures clearly visible.

In the Hutt Valley there is to the writer's knowledge only one instance where offset at a fault plane is visible. This is on Haywards Road, where the Haywards Gravel Formation (Stevens, 1956) has been set against greywacke and a sharp reverse fault produced. In other areas actual fault planes are unrecognizable owing to lack of exposures and prevalence of shattering in the rocks. Miller reported similar problems in southern California (1941: 89).

2. Vertically displaced strata.

This criterion can be applied to a few cases where alluvial gravels straddle the Wellington Fault Zone but elsewhere it has no application because of the lack of cover beds and the homogeneity of the terrain. Further, and so far as any but recent faults are concerned, fault-line erosion adjacent to faults has obliterated most primary fault features, including evidence of offsetting of superficial deposits.

3. Recent fault scarplets.

These structures, which dislocate the present-day erosional or depositional land surface, are comparable to faults cutting unconformities or bedding. In this context “fault scarplet” is preferable to “fault trace”, as “trace” is a general (geometric) term which should refer to the intersection of a fault plane with any kind of surface, including bedding or fault planes as well as the topographic surface. Recent fault scarplets along the line of the Wellington Fault occur at Emerald Hill (Fig. 2) and southern Wellington.

4. Vertically displaced erosion surfaces.

Miller (pp. 90–91) found this criterion to be of the utmost value in the determination of faulting in southern California. He states (p. 90):

“. relatively long, straight scarps, separating such old erosion surfaces sharply at different levels, are almost as good as positive stratigraphic evidence of faulting.”

Identification of dislocated remnants of an old erosion surface (the Kaukau Surface) provides the key to fault identification in the Hutt Valley. These remnants are readily distinguished by their senile topography and the great depth of weathering present on their surfaces, so that positions and throws of many faults are well defined.

In the special circumstances of unfossiliferous greywacke country and Pleistocene faulting, geomorphological mapping of faults is superior to the more customary procedures of fault determination. Conventional methods deal with isolated points in space (i.e, outcrops) and yet allow the joining of such points to represent bedding or fault planes. On the other hand, geomorphological procedures deal with dislocations of a visible landscape surface which can be identified over much of its extent.In the Hutt district the Kaukau Surface is well defined and of considerable area, and dislocation of this surface is revealed by the “stepped” topography on either side of the Wellington Fault and frequently by the presence between “steps” of strong fault lineations.

5. Horizontal displacements.

The greatest disadvantage of mapping faults in terms of surfaces is that the method can only be applied to relatively recent faulting. This does, however, aid the study of faulting processes, for it enables the selection of faults of only one period and also allows the study of rates of earth movement. Further advantages lie in the

fact that transcurrent movements of only a few yards can be readily detected and in so far as the surface of reference, the earth's surface, is everywhere exposed, most of the faults over an area can be examined. Allowing for the restriction to faults of one age, the geomorphic method is the most certain of widely applicable methods of measuring transcurrent movement. In areas adjacent to that studied here, horizontal offsets have been recorded by Cotton (1950, 1951) and Adkin (1954), and it is generally accepted that the Wellington Fault and several other faults in the Wellington area are transcurrent.

6. Shatter Zones.

In the greywacke terrain of the Wellington Peninsula, erosion is controlled and lineations determined by intimate emposed weaknesses rather than by inherent sedimentary variations in the strength of strata. Despite the segregation of argillites and arenites into rhythmic beds in the Wellington greywackes, the succession is on the large scale homogeneous and of uniform lithology and variation of strength across bedding is slight. Thus the controlling effect of bedding on erosion is much reduced and the landscapes may be described as tending towards isotropy to erosive processes. Furthering this tendency is the intense shattering which pervades almost all the greywacke sandstones and renders the hardest bands as weak to attrition as the softest Still further, in the young topography of Wellington Province the steep gradients favour the transport of large rock particles and allow erosion of shattered hard beds as well as soft. Finally it seems that transcurrent faulting imposes intense local shearing stresses on the rocks so that faults are marked by zones of extreme comminution. In a broadly isotropic environment this cataclastic effect is directly reflected by erosional fault-line features such as stream lineations and notches in crests and spurs.

7.Alignment of saddles.

In a full account of geomorphic expressions of faulting, Cotton (1950: 739) maintains:

“… jogs and notches, according to the direction of down-throw, remain in the landscape after erosion has eliminated all geomorphic traces of faulting in adjacent valleys; on resistant terrains they may survive into full or late maturity of dissection, whatever the prefaulting form of the surface or its postfaulting history.”

To the west of the Wellington Fault notched spurs and aligned saddles are very well developed. Such features are fault-line features sensu stricto, for an “etching-out” of a fault pattern by subsequent erosion has occurred.Faults distinguished by such etching characters may be of any age and should not be confused with recent faults which are generally identified as dislocations of topographic surfaces.

8. Stream lineations.

Commonly it is only the river pattern of a greywacke terrain which gives any direct indication of a fault pattern. Valleys bear little relation to the strike of inclined or folded strata and in many places rivers follow zones of obviously fault-shattered rock. The straight stretch of the Tauwharenikau River, Tararua Mountains (N. Z. M.S. 1, N161), provides a good example of deep etching of a shatter zone. Here recent fault traces and fault-controlled saddles have been recognzed to the north-east and south-west of the stream lineation and also in the river valley. Though on a smaller scale, similar stream lineations occur to the west of the Wellington Fault and in particular along the line of the Liverton Fault. In the latter examples shatter belts mapped in the field line up with stream lineations, spur or ridge notches and jogs, and similar features.(Pl. 44, Figs. 1, 2, 3.)

Cotton (1950: 746) has discussed the theory of river guidance by “shatter belts” in these words:

“In New Zealand the fault-line erosional hypothesis has been called upon to explain alignment of some valleys near Wellington with faults and crush zones.… and generally it has been assumed that these faults zones are ancient.”