Thomson. — Diastrophic Correlation and Districts in the Notocene. 405 



greensands, limestone, greensands, mudstones, sands and gravels ; and he 

 has even attempted to correlate beds in different parts of New Zealand 

 by their height above the limestones there developed. He has now pro- 

 posed a classification of the post-Cretaceous members of his system on 

 the basis of faunas, characterized by their percentage of Recent species. 

 With this method of characterizing faunas I shall deal below. Meanwhile 

 it is satisfactory to note that in adopting the principle of successive faunas, 

 employed by Hutton, he has returned to sound lines. Concerning his 

 Waitaki series, which appears to be the equivalent of the Oamaruian, he 

 states, " The dominant fact emerges that the species are so similar through- 

 out that the beds obviously belong all to one series." If this conclusion 

 is maintained, as I believe it will be, it of course justifies the use of a series 

 name to include them. It is based, however, on small collections from few 

 localities for each stage, except in the case of the Awamoan, and takes 

 into cognizance only the molluscan fauna. In my opinion it is premature 

 to attempt to revise the earlier groupings of the Tertiary rocks into series 

 by their faunas without a much more exhaustive statement of what those 

 faunas are. 



My own proposal was for a series of unit or stage names for the smaller 

 well-marked rock divisions, which have been recognized in all earlier classifi- 

 cations, leaving their grouping into series or systems until our palaeonto- 

 logical knowledge is more complete. Such a system of stage names will still 

 have a permanent value after the grouping is possible, unless the divisions 

 prove too large for zonal purposes. It is, of course, also based on the suc- 

 cession of faunas, as Marshall himself has helped to show by his statement 

 of the increase of the percentage of Recent species in successively younger 

 beds of his series ; but it neglects intentionally the grouping of the units 

 into series by major faunistic considerations, because this is considered 

 premature. It may be a minor diastrophic accident that the succession 

 at Oamaru commences with the Ngaparan. The fauna of the preceding 

 stage may also be such that it should be grouped in the same faunistic 

 series as the Oamaruian stages. 



The two sets of local names for divisions of our Tertiary rocks are not, 

 therefore, necessarily in conflict. One is a set of names for stages, the 

 other a set of names for faunistic series. Both are based on the principle 

 of a succession of faunas independent of considerations of conformity and 

 unconformity. It remains to be considered whether the principles by which 

 the divisions are selected and the names chosen are sound. 



The only principle of division adopted by Marshall is that of the per- 

 centage of Recent molluscan species in the different beds. In passing, 

 it may be observed that the percentages of Recent species adopted by 

 Lyell included also the Brachiopoda, which are unimportant in the Euro- 

 pean Tertiary, but assume a much greater importance in New Zealand. 

 To use the percentage of Recent species as a sole principle of division seems 

 to me premature. The lists of fossils published during recent years do not 

 cover one-tenth part of the determinations made by Mr. Suter for the 

 Geological Survey on old and new collections, and for no single bed that 

 I know of has collecting been so thorough that a further visit has not 

 added to the list of species. We do not know accurately the percentage of 

 Recent species for any division of the New Zealand Tertiary. Even if 

 we did, the results could not be used with confidence in the correlation 

 of one bed with another without a further analysis. The percentages 

 may be different for the species which lived above and below the 100-fathom 

 line ; they may be different again for the faunules which inhabited 

 sandy, muddy, glauconitic, or calcareous bottoms. Further, it would be 



