280 Transactinns. 



Basin ; the cliffs at Gore Bay, where well-cemented gravels are involved in 

 a syncline ; the western side of the Trelissick Basin, specially in the Hog's 

 Back Creek ; between the Pudding Stone and the North Ashburton River ; 

 and in South Canterbury between the Tengawai and Pareora Rivers. It is 

 probable, too, that the deeper gravels encountered in the bore at Chertsev 

 belong to this series, the indications of petroleum coming from plant-remains 

 which elsewhere have formed lignite.* Just below the Rakaia Gorge, where 

 great thickness of gravels has been exposed, there is an underlying set of beds 

 which are more strongly oxidized than the covering strata, and they may 

 perhaps be assigned to a series older than the prevailing shingle beds of the 

 plains. Although this criterion is perhaps an unsatisfactory one on which 

 to base a determination of relative age, yet it has been applied in Switzerland 

 in order to differentiate the gravels of the older glacial series of that region. 



General Conclusions as to the Origin and Age of the Beds, and 

 Relation to the Gravels of the Canterbury Plains. 



The materials of which these gravels are composed have been derived 

 almost entirely from original greywackes. No limestone was noted among 

 them except in the case of the beds in the North Kowai. Occasional pebbles 

 of basalt also occur, such as might have been derived from areas where such 

 rocks are known to exist. A siliceous sandstone, white in colour and forming 

 rounded masses, which could not be traced to its source, also occurs freelv 

 in the gravels of the Mount Grey district. These are perhaps masses of sand- 

 stone which have been loosely cemented by processes analogous to those 

 which have formed the sarsen stones, or " Chinamen," as they are called by 

 miners, of the schist areas of Central Otago. 



The subangular nature of the pebbles shows that the greywacke land 

 must have been in close proximity to the area of deposit. The absence of 

 large pebbles suggests that it was of moderate relief, though it might have 

 been the outlying portion of a more elevated tract. The gravels contain, 

 however, no suggestion of a glacial or fluvio-glacial origin ; they are just 

 such gravels as might have been brought down by the present Ashley or 

 Waipara Rivers, which have no connection with glaciers. The origin of 

 the limestone constituent can be traced exactly, as exposures of limestone 

 of similar nature occur within a short distance of the area where they have 

 been deposited ; but these limestone pebbles occur low down in the series and 

 disappear at higher levels, so that the uppermost beds must have been derived 

 from areas where limestone does not exist. Although the lower members of 

 the series are undoubtedly marine, the upper members were in all probability 

 deposited under estuarine conditions or actually on a land-surface. 



The determination of the age of the Kowai series is a matter of some 

 difficulty. The unconformity in the Grey River shows that it is certainly 

 post-Miocene, and in the Lower Waipara Gorge beds occur under the gravels 

 with a fossil content which shows them to be upper Pliocene (Speight, 1914, 

 p. 300) — that is, beds which form the upper part of the Motunau series. 

 Therefore we may reasonably infer that the Kowai series is either upper 

 Pliocene, if no unconformity exists between two sets of beds, or Pleistocene, 

 if an unconformity is demonstrable. The Pliocene beds of the lower Waipara 

 are perhaps the uppermost beds of a conformable Cretaceo-Tertiary series. 



* Pieces of carbonized bark have recently been obtained from a depth of 1,900 ft. 

 in this bore. 



