116 Transactions. 



How, then, can Cotton's alternative explanation of a coastal plain 

 followed by " the remaining events .... the same as those outlined 

 in the previous explanation " be possible 'i Obviously it could not. The 

 secular subsidence would carry the " coastal plain of subaqueous sands," 

 along with the old land-surfaces mentioned above, far below the present 

 surface, and it woiild be hidden either by continuous river-gravels or by 

 blown sand, and the lowland would approximate to that suggested by 

 Cotton in his first explanation. This, I think, disposes of the alternative 

 explanation. 



Since the gravel fans of the larger rivers are below and not upon the 

 sandstone formation, the prograding of Cotton's strand-plain had to rely, 

 in face of subsidence, on the supply of sand and the detritus of minor 

 streams. But proof has been given above that the river-fans were built 

 not on a subsiding maritime area, but on a stationary inland surface. 

 Cotton's principal explanation is thus as untenable as the alternative one. 

 If, however, these difficulties can be explained away, further evidence is 

 furnished by the texture and structure of the sandstone formation. 



The variation in the composition of the sandstone formation in a north- 

 east and south-west direction — viz., from friable pumiceous sand north of 

 Tokomaru to relatively compact greywacke-derived quartzose sand south 

 of that locality — cannot be explained by the aeolian hypothesis ; but if the 

 variable material is regarded as shallow-water deposits laid down along a 

 shelving coast to form a potential coastal plain no difficulty presents itself. 

 Similarly, by the aeolian theory, the sand carried farthest inland would 

 be the finest, or at least as fine as that at the source of supply — i.e., along 

 the prograding shore-line. But this is an inversion of the actual facts. 

 All along the coastal lowland, and in the quartzose areas more especially, 

 the sandstone is coarsest along the inner margin, grading to a finer texture 

 towards the present coast-line — facts strongly supporting the marine- 

 deposition theory and quite adverse to the aeolian. 



Perhaps the most striking features of the sandstone formation are the 

 cross-bedding and delicate lamination. The dunes of blown sand that lie 

 nearer the present coast-line do not exhibit a similar structure, and it is 

 in this respect that the two formations are in such strong contrast, though 

 the compact texture of the one and the looseness of the other is equally 

 striking. This diversity of structure under similar, if not identical, cUmatic 

 and geographical conditions points to dissimilar origins for the sandstone 

 and the blown sand : the former must thus be a subaqueous deposit. 



I agree with Cotton that pseudo -stratification is sometimes present in 

 the sandstone ; but there is also quite frequently a well-defined true strati- 

 fication. Alternations of thin beds of loam or clay interstratified with 

 thicker ones of sandstone are quite common. Occasionally a sandstone 

 stratum is intersected by two sets of joints, and breaks up into cubical 

 blocks while in situ, while the layers above and below are compact. In 

 these and other ways the presence of true stratification is revealed, and I 

 contend that the structure of the sandstone formation adds to the weight 

 of evidence of its having originated as a marginal marine deposit uplifted 

 to form a young coastal plain. 



I have but little hesitation in affirming that the peneplanation of dunes 

 of blown sand* is a physical impossibility ; such, in any case, is the verdict 



* C. A. Cotton, loc. cit. (1918), p. 216. 



