Thomson. — Diastrophic Correlation and Districts in the Notocent 397 



Art. XXX. — Diastrophic and other Considerations in Classification and 

 Correlation, and the Existence, of Minor Diastrophic Districts in the 

 Notocene. 



By J. Allan Thomson, M.A., D.Sc, F.G.S., Director of the Dominion 

 Museum, Wellington, New Zealand. 



[Received by Editors, 30th December, 191b' ; issued separately, 30th November, 1917.] 



Contents. 



I. Diastrophic Considerations in Correlation, and the Existence of Minor Dia- 

 strophic Districts in New Zealand during Late Cretaceous and Early Tertiary- 

 Times. 

 II. Supplementary Statement of Principles involved in Classification. 



III. An Age-name for the "Covering Strata" or "Younger Rock-series : ' of New 



Zealand. 



IV. New Adjectival Names applicable to the Divisions of the Notocene. 

 V. A New Name for the So-called Quaternary Rocks of New Zealand. 



VI. Appendix I : Description of Pachymagas abnormis n. sp. 

 VII. Appendix II : A Hypothetical Case illustrating the Effect of Immigration on the 

 Percentage of Recent Species. 

 VIII. List of Papers cited. 



I. Diastrophic Considerations in Correlation, and the Existence 

 of Minor Diastrophic Districts in New Zealand during Late 

 Cretaceous and Early Tertiary Times. 



Correlation by lithology implicitly involves diastrophic considerations, 

 but the first explicit use of these in the classification and correlation of the 

 younger rocks of New Zealand occurred in a paper by Marshall, Speight, 

 and Cotton (1911). The thesis put forward by these writers after an exami- 

 nation of several critical localities was that no unconformity exists within 

 these younger rocks, which were deposited in a single cycle of depression 

 and re-elevation. In different localities the basal beds of the series vary in 

 age from Cretaceous to Miocene, owing to overlap during depression on a 

 surface of high relief ; but the middle member, the limestone, was deposited 

 at the period of maximum depression, apparently " early Oligocene," and 

 is therefore contemporaneous throughout the country.* In support of this 

 principle of correlation a paper by T. C. Chamberlin (1909), entitled 

 " Diastrophism the Ultimate Basis of Correlation," was cited in a foot- 

 note. The authors mentioned their intention to state fully the palaeonto- 

 logical side of the question in future papers, thereby admitting to some 

 extent that the palaeontological evidence was not adequately known, but 

 would be expected to fall into line with the diastrophic considerations. 



Diastrophism is defined by Chamberlin and Salisbury (1909) as including 

 all crustal movements, whether slow or rapid, gentle or violent, slight or 

 extensive. In claiming that these movements form the ultimate basis of 

 correlation, Chamberlin (1909) gives reasons for accepting the periodicity 

 of the great world-warping deformations, while admitting the adjustment 

 of minor stresses at other times, producing intercurrent departures from 

 the strict tenor of the great systematic movements. The base-levelling 



* The contradiction implied in this statement is presumably only a slip on the 

 part of the authors. The highest basal beds should not be later than Oligocene on their 

 theory. Marshall now classes the limestone as Miocene. 



