400 Transactions. 



sea-advance followed, and it was not until a comparatively late Tertiary 

 period that a new cycle of major diastrophism commenced with the 

 Kaikoura orogenic movements.* Between these maxima of diastrophism 

 were laid down those sediments, ranging from Middle Cretaceous (Utatur) 

 to late Tertiary (Wanganuian), which were called by Marshall and his 

 colleagues the younger rock-series of New Zealand, and named by Marshall 

 the Oamaru system .f Previous classifications had not brought out the 

 close diastrophic relationship of this group of rocks, and in this respect the 

 paper in question marked a great advance. 



Cotton (1916) has recently attacked the study of the younger rocks 

 from a physiographical and structural point of view, and his conclusions 

 as to the surface on which the beds were laid down are diametrically opposed 

 to those reached in 1911. After the folding of the middle and lower Meso- 

 zoic rocks, he concludes that the surface was reduced practically to a pene- 

 plain before the deposition of the covering strata in several districts. The 

 evidence for this is very clear in the case of the Ngaparan rocks of North 

 Otago and South Canterbury, and the still younger rocks of the Aorere 

 Valley and the Gouland Downs. Cotton (1913) originally suggested a 

 similar state of affairs for the Middle Cretaceous covering rocks of the 

 Clarence Valley, but it is not to be expected on theoretical grounds that at 

 this date peneplanation was complete, nor does the very thick series of con- 

 glomerates, sandstones, and mudstones of this age support the suggestion. 

 The presence of thick beds of greensand in the Senonian of North Canter- 

 bury, however, makes it likely that by this date the land surface had lost 

 its former great diversity. Speight (1915) from an analysis of the nature 

 of the sediments in Canterbury has come to a similar conclusion. If this 

 view is correct, and if the great differences in the age of the basal covering 

 beds in different districts are admitted, a view for which the palaeontological 

 evidence is overwhelming, it follows, as I pointed out in 1914, that the 

 earth and sea movements which permitted the deposition of these beds 

 were not purely regional sea-advance, so far as the New Zealand area is 

 concerned, as is assumed in the simple diastrophic theory, but movements 

 irregular in their effects. Depression below sea-level occurred at an earlier 

 date in some regions than in others. In north-east Marlborough it occurred 

 in the Middle Cretaceous, in North Canterbury in the Upper Cretaceous, 

 at Kaitangata between Senonian and Ngaparan, in South Canterbury and 

 north-east Otago in the Ngaparan, in the Lower Awatere district in the 

 Upper Oamaruian, at Maharahara in the Wanganuian, and so on. A still 

 stronger line of evidence than the period of commencement of depression 

 below sea-level is afforded by a consideration of the periods at which de- 

 position ceased owing to sea-retreat. Even if the different age of the sea- 

 advance in the different districts was due in some measure to differential 

 relief, the irregularities in the surface would have been obliterated by 

 sedimentation, and deposition should have ceased, under uniform regional 

 conditions, approximately contemporaneously in all areas, whatever the 

 date of its commencement. Nevertheless, the youngest marine deposits of 

 the Clarence Valley are Oamaruian (stage uncertain), those of North Otago 

 are Awamoan, those of North Canterbury (the Motunau beds) are probably 



* Cf. Cotton, 1916. The Kaikoura movements did not commence everywhere at the 

 same time, and probably the Awatere and Clarence areas were the first to be affected. 



f Marshall has not yet included the Middle Cretaceous rocks of the Clarence and 

 Awatere Valleys in his Oamaru system, but it is difficult to see how otherwise he could 

 deal with them. 



