8 W. N. BENSON 



tions appear to be realized in some measure in the facts observed in 

 field study. The microscopical structure of the schists is indicative 

 of strong lateral thrust rather than static metamorphism, and an 

 excellent series of gradational structures which link them with the 

 graywackes has been obtained by Marshall. Moreover, the 

 apparent absence from the graywackes of any material which seems 

 to have been derived from the schists is a striking feature, con- 

 sidering their close association. 



The "Notocene" Sediments.— The record of the later Cretaceous 

 and Tertiary times has as elsewhere received diverse interpretations. 

 The simplest among current views considers that the whole series 

 is conformable throughout. Overlap on to an evenly subsiding 

 but irregular surface accounts for the difference of age of the basal 

 beds in different regions. The period of greatest submergence 

 was the period when limestone was deposited, so that the Kme- 

 stones in all regions must be considered as of the same age. They 

 are succeeded by beds of a clastic character, indicating the return of 

 shallower conditions. On other hypotheses the whole group of 

 formations is divided up into several unconformable series, but 

 the ages assigned these series, and the horizons at which the uncon- 

 formities were recognized, have been different in the statements 

 of different writers, or at different times in the statements of one 

 writer. While, therefore, there has been little dispute as to the 

 succession of strata in any region, the history of the whole period 

 throughout New Zealand has remained obscure. 



Two new conceptions have been advanced during the last 

 decade. Thomson has suggested the existence of "diastrophic 

 provinces," i.e., regions throughout each of which the tectonic 

 history has been the same, though differing from that of adjacent 

 regions. On this hypothesis, the difference of age of basal beds 

 depends on the overlap of formations on a subsiding uneven bed 

 but also on the different periods at which subsidence commenced 

 in the various provinces. The limestones are not necessarily 

 coeval throughout New Zealand, but represent merely the rock 

 formed at the time or times of maximum submergence in each 

 particular province, for in some districts more than one horizon 

 of limestone is present. So also the regression of the sea occurred 



