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break into such fossiliferous rocks in north-eastern Otago. The Geo- 

 logical Survey and the majority of other geologists have held that the 

 schists are ancient, and must be separated by obscure unconformities 

 from these fossiliferous rocks. Dr. Marshall has, however, emphasized 

 the complete absence of any material derived from the schists in the 

 adjacent greywackes, and has described in detail an apparent passage 

 between the unaltered greywacke and the mica-schist, traced along 

 a line of sectior. in the southern flank of the anticline namely, from 

 Balclutha to Lawrence, a distance cf about twelve miles. He concludes, 

 however, that the schistose structure is net a direct mechanical effect 

 of pressure, there being little sign of crushing or strain, but is rather 

 the effect of chemical action stimulated by mechanical pressure, which 

 has caused the regular orientation of the secondary crystal-grains 

 developed, and especially of the flakes of mica which replace the alkali- 

 feldspar. On the other hand, the longer diameter of the quartz-grains 

 is generally perpendicular to the plane of schistosity. 



In other regions, particularly in north-western Ota.go, though it has 

 been asserted that there is an observable transition of greywacke into 

 schist, this is not supported as yet by such detailed observations, and 

 in places there seems, instead, to be a rather sharp break between them, 

 so sharp that it can be detected by differences in the topography. 

 In supporting Dr. Marshall's general views as to the age of the schists, 

 the writer has suggested a working hypothesis of the structure of the 

 apparent anticline, which may also be found to explain the passage, 

 sometimes gradual and sometimes very sharp, between the unmeta- 

 morphosed and metamorphosed rock-types. In this it is suggested 

 that the " anticline " is not simple, but is an arched packet of 

 recumbent sheet-folds, the schistose structures of which were de- 

 veloped by recrystallization during folding under the weight of the 

 overlying folds. The upper sheets would therefore be noticeably less 

 metamorphosed. Subsequent block-faulting would bring the less meta- 

 morphosed higher sheets down to the level of the more metamorphosed 

 lower sheets. Out of this " mosaic of differentially moved blocks " the 

 general peneplain was. cut at the commencement of the Tertiary times, 

 and erosion following the later post-Tertiary (?) crust - movements 

 (which moved diversely the same series of crust-blocks) has produced 

 topographic forms that vary with the lithological character of the 

 blocks, a suggestion which incorporates the conclusions of Professor 

 Cotton concerning the geographic evolution of Central Otago. The 

 difficulty in the way of testing this hypothesis is the absence of 

 any readily recognizable sedimentary series within the schists and 

 the adjacent rocks, and much investigation, therefore, will be neces- 

 sary before it can be either accepted or rejected. 



W. N. BENSON. 



