298 Transactions. 



Hector* included the lower rocks of Hutton's Oamaru system in his 

 Cretaceo-tertiary division. Some of the higher strata he placed in the 

 Upper Eocene, and a few of the highest in the Lower Miocene. 



Parkf has lately placed the whole of the Oamaru beds in the Miocene. 



Marshall, Speight, and CottonJ have lately stated that the Oamaru 

 rocks represent a portion of a conformable series extending in age from the 

 early Cretaceous to the late Miocene. This view has also been put forward 

 by Marshall in the " Regional Geology "§ and in the " Geology of New 

 Zealand. "II 



This general statement of the various opinions that have been expressed 

 in regard to the age of the Oamaru rocks shows that despite their generally 

 fossiliferous nature and the clear character of their stratigraphy it is still 

 possible to interpret the facts in terms that are widely different, if not, indeed, 

 wholly opposed to one another. It is evident that in such a district, where 

 there are few or no difficulties in interpreting the stratigraphy in the field, 

 actual observations may be relied on for definitely determining the true 

 relations of the strata. There has, however, been a tendency to neglect 

 the clear and per se unmistakable field evidence, as it has been held that the 

 fossil remains found in the various members of the series of rocks in the 

 district are of such a nature as to indicate that different geological periods 

 are represented by them. Such opinions have caused some observers to 

 break up the series into integral portions, and to endeavour to find structures 

 in the field that might support the conclusions that were derived from 

 palaeontological work. It is not the intention of the present authors to 

 quote and discuss the statements that have been made in regard to the evi- 

 dence ofiered by field-work in favour of stratigraphical breaks in the rock- 

 series. Some reference has already been made to this aspect of the subject 

 iu the paper by Marshall, Speight, and Cotton on the younger rock-series 

 of New Zealand. It need only be remarked here that those who have split 

 up the series into different geological pei'iods show few points of agreement 

 among themselves. 



It is believed by the present authors that tlie difficulties which have 

 presented themselves from the palaeontological standpoint have resulted 

 from a failure to recognize the fall significance and effect of a relatively 

 rapid movement of depression during the deposition of the sediments. 

 The succession of the material from conglomerate through sands, green- 

 sands to limestone shows that the effect of depression in deepening the 

 water was far more important than the effect of deposition in shallowing 

 it. The natural result of this was to cause a great overlap of the upper 

 strata over the lower, a rapid lateral change in the nature of the strata, 

 and a complete change of biological station at various points along a single 

 vertical line. The effects of such important influences as these must be 

 clearly sorted out before any reliance can be placed upon conclusions derived 

 from the collection of fossils. 



Finally, the collections of fossils have Ijeen most incomplete, and in 

 some cases it appears that identifications have been most unsatisfactory. 

 The failure to identify fossils with accuracy could only be expected, for 

 hitherto the nomenclature and synonymy have been most perplexing. 



* " Handbook of New Zealand Geology," pp. ."SI -59. 



+ " Geology of Now Zealand,"" p. 1 Kl Whitcoinhc aiiil Tumi)-;. ( hristchurch. 

 N.Z., 1911. 



I Trans. N.Z. Inst., vol. 4:J, 1911, p. 393. 



§ 'Regional Geology." J911, band 7, i. pp. 22-23. < 'ail Winter. Hi-idflhern. 



II Tieology of New Zealand."" p. 188. d'ovcnimcnt rrintci. 1912. 



