Thomson. — Diastrophic Correlation and Districts in the Notocene. 399 



was so rapid as to produce marked overlap without allowing for the lower- 

 ing by erosion of the land surface during deposition which the deposits 

 themselves indicate. 



Willis (1910) in discussing the periodicity of diastrophism finds it 

 necessary to make certain qualifications. ' The general law should be 

 supplemented by one which recognizes unlike dynamic histories of different 

 oceanic regions. It may be stated thus : The phenomena of diastrophism 

 are grouped according to several distinct dynamic regions. Each region 

 has experienced an individual history of diastrophism, in which the law of 

 periodicity is expressed in cycles of movement and quiescence peculiar to 

 the regions. The cycles of one region have been, however, to some extent 

 parallel, though not conterminous, with the cycles of other regions, and thus 

 major cycles of world-wide conditions are constituted by coincidences of 

 regional conditions." 



There is a considerable difference between these points of view so far as 

 the world-wide application of diastrophic criteria are concerned. According 

 to Chamberlin's view, the great deformations are world-warping, and it 

 is the effect of these movements and of subsequent sedimentation through 

 base-levelling on the level of the sea the whole world over which is empha- 

 sized as important for correlation. According to Willis's view, the existence 

 of independent dynamic districts means that emergence of land in one dis- 

 trict ma) T at any particular time more or less compensate for the filling of 

 the sea-basins by sedimentation in another. The rise and fall of the sea- 

 level, so far as this is effected by displacement simply and not by gravita- 

 tional attraction, will be the sum of the displacements produced by different 

 great deformations, which are not necessarily in the same phase; and the 

 sedimentary cycles of the different districts may be in different stages, and 

 differently effected by the world-wide changes in sea-level. It is only when 

 the great deformations are approximately in the same phase that the deposits 

 can be homologous the whole world over. This latter view seems better 

 adapted to explain the stratigraphical diversity of different parts of the 

 world, the greater duration of sedimentary cycles in one part than another, 

 and the frequent impossibility of bringing important groups of sediments 

 into fully developed cycles of sedimentation. 



When it comes to the discussion of actual problems of correlation the 

 specific criteria of diastrophism may at times appear to conflict with the 

 criteria of palaeontology, and in such a case Ulrich (1911) contends that 

 the palaeontological evidence is the more trustworthy. This, indeed, seems 

 axiomatic. The physical conditions controlling the deposition of beds of 

 a given lithological character may be reproduced by diastrophism ; the 

 life accompanying the recurring conditions may be similar, but can never 

 be exactly the same, owing to the fact of organic evolution. The criteria 

 of palaeontology as at present developed are more delicate, and permit 

 a more certain discrimination of apparently similar but really different 

 effects than do the criteria of diastrophism. The latter are affected by 

 the intercurrent departures within the cycles, departures which are only 

 revealed by the criteria of stratigraphy and palaeontology. 



In New Zealand about the early Cretaceous* there was a great diastrophic 

 deformation, with wrinkling of the earlier Hokonui and so-called Maitai 

 rocks and the formation of an extended land surface. Base-levelling and 



* The ammonite beds of Kawhia lie on the dividing-line between Jurassic and 

 Cretaceous ; the belemnite beds and plant beds of Waikato Heads are later, and generally 

 ascribed to the Wealden. The deposition of these beds apparently preceded the close 

 at least of the great post-Hokonui deformation. 



