Speight. — The Intermontane Basins of Canterbury. 337 



These rest everywhere in the Canterbury region on folded sedimentaries 

 of Trias-Jura age or on voleanics which have penetrated and overlie these 

 sedimentaries. It must be noted, however, that the sequence just quoted 

 is rarely complete, and that, as is natural in a country which has been 

 exposed to active erosion for a considerable period, it is the lower members 

 which are most frequently in evidence. The number of remnants of these 

 beds is somewhat large, and they are usually placed in basins either par- 

 tiallv or whollv surrounded by the Trias-Jura rocks. The chief of these 

 basins are the following : Hanmer Plains, Culverden Plain, Castle Hill 

 basin, the Md-Waimakariri, the Upper Kakaia, Lake Heron, Mid-Rangitata. 

 Upper Pareora ; but there are others of small size which have an important 

 bearing on the problem. 



The two suggestions that have been put forward to explain their occur- 

 rence are, — 



1. They are the remnants of a widely distributed cover of Tertiary 

 beds which once masked the greater part of the surface of the country. 

 Since thev were weak structurally, they have been removed from the higher 

 and more exposed parts of the country by ordinary erosive agents, such as 

 frost and rain, but more especially by the abrasion of the great glacier,-, 

 which in Pleistocene times filled the valleys. The isolated fragments of 

 this covering are only to be found in positions w T here they were more or 

 less shielded by the form of the ground from these erosive agents. 



2. They have always been in the form of discontinuous deposits, and 

 represent materials which have been laid down in isolated areas which 

 were invaded by the sea, the basins having been eroded in pre-Tertiarv 

 times, and were, during the time of deposition, bays, gulfs, or straits 

 belonging to a more open sea ; and these basins had even at the time 

 • if deposition a form closely approximating to that which they have at 

 present. 



The first suggestion has found its strongest support up to the present 

 from Cotton. There are suggestions, however, in the writings of other - 

 that the idea had occurred to them. Cox, for instance, in his " Report on 

 the Geology of the Clent Hills District " (" Report of Geological Explora- 

 tions," 1877, p. 107), notes the wide extent of the Cretaceo-tertiary series 

 in that district, and concludes that they have not filled valleys of erosion 

 owing to their presence at higher levels. Later, however, he departed 

 from this opinion, for in his report on the same district in 1884 (" Report 

 of Geological Explorations for the Year 1884," p. 43) he evidently regards 

 the basins in which the Awamoa and Pareora beds were laid down as having 

 much the same form as at present, for he considers the sea had access to the 

 basin by way of the Rangitata River and the Pudding-stone Valley, and 

 neither by way of the Rakaia nor by the Ashburton Gorge, which was not 

 cut at that time. 



Park apparently occupies a middle position, which results from his 

 division of the Cretaceo-tertiary sequence of beds into two great series 

 with an unconformity between them. This he places finally between the 

 glauconitic limestone (Weka Pass stone) and the argillaceous limestone 

 (Amuri limestone). He regards the series closed by the latter beds as his 

 Amuri system, which was laid down in basins of previous formation, for he 

 says (" Geology of New Zealand," p. 88), " The Cretaceous beds, although 

 deeply involved in the faults that follow the foothills of the Inland Kai- 

 kouras, take no part in the tectonic arrangement of the rocks of the Hoko- 

 nui system, but rest against them as marginal deposits that follow the strand 



