404 Transactions. 



The histories of the individual diastrophic districts thus indicated within 

 the New Zealand area are not in all cases parallel. In some there has been 

 a conformable series of sediments deposited ; in others there have been 

 earth-movements of different ages, producing unconformities in the series. 

 There is no single unconformity that has been proved to be common to all dis- 

 tricts. Hence any classification that shall be applicable to the whole country 

 cannot be made to depend on the presence or absence of unconformities. 



II. Supplementary Statement op Principles involved in Classifi- 

 cation. 



It appears at first sight unfortunate that two new sets of local names 

 applicable to the divisions of the Tertiary in New Zealand should be pro- 

 posed in the same volume of the Transactions (Thomson, 1916, No. 1 ; 

 Marshall, 1916, No. 2). As the principles given for selecting them are, 

 however, fundamentally distinct, the adoption of either of them will doubtless 

 be determined ultimately by the acceptance given to those principles, and 

 I do not desire to insist unduly on the claims of priority which attach to 

 my own proposals It seems desirable, however, to state more fully the 

 principles which are at issue, as until there is agreement concerning these 

 it is hopeless to expect that any system of nomenclature will meet with 

 acceptance The analysis shows that there is no necessary conflict between 

 the two proposals, but that Marshall's procedure is somewhat premature 

 and his nomenclature not satisfactory 



A distinction must be drawn in the first place between classification 

 and correlation. Marshall's principle of classification is also made the 

 main principle of correlation. The principles of correlation are numerous 

 and intricate, especially as applied to Tertiary rocks, and they must be 

 used as they are found applicable, and, if necessary, independently of any 

 principles used in classification. The latter are much more simple. 



The first point of my paper was that correlation with the divisions of 

 the European classification is a matter of considerable difficulty in New 

 Zealand, and one that has not been at all adequately discussed except 

 for a very few groups of organisms, and then only for fossils from a very 

 limited number of districts. The conclusions reached are contradictory, 

 and none is entitled to outweigh the others. Consequently we begin at the 

 wrong end when we call our rocks Eocene, Miocene, or Pliocene. There 

 is no finality in such a procedure. Marshall's Miocene is not the same as 

 Hector's or Hutton's, and yet all these authors were in practical agreement 

 as to the relative position within the New Zealand succession of the rocks 

 they so termed. The order of superposition of our Tertiary rocks is not 

 in doubt in practically any district where there is a series developed. Let 

 us, then, frame a classification with local names which are non-committal 

 as far as European correlation is concerned. So far Marshall appears to 

 be in agreement : " It would obviously be better to use New Zealand 

 local names for the horizons of the Tertiary rocks of this country." 



Geological classification is no longer governed by considerations of 

 conformity or unconformity, but by the succession of faunas. This was 

 first established as an empirical conclusion, and later received a logical 

 basis through diastrophic considerations. Diastrophism is now recognized 

 to be cyclic, and to be a prime cause of the changes of fauna. The inter- 

 pretation of diastrophic history, however, depends again on palaeontological 

 and stratigraphical studies, and, of the three kinds of criteria available, 

 those of palaeontology are found to be the least open to misinterpretation. 



Hitherto the only subdivisions recognized by Marshall within his Oamaru 

 system have been the unit rocks of the series — conglomerates, sandstones, 



