Speight. — The Inter montane Basin* uf Canterbury. 341 



2. Pre-Cainozoic dissection ; valleys formed principally along lines of 

 fracture of fault. Some features of many of the existing valleys and basins 

 impressed. 



3. Early Cainozoic subsidence, with infilling of valleys; marine trans- 

 gression, the sea invading some of the depressions 



4. Middle Cainozoic uplift started, continuing with minor fluctuations 

 to the present time. Faulting, with probably some warping, during middle 

 and late Cainozoic times. Many of the old lake basins modified. 



5. Advance of glacier conditions in late Cainozoic ; existing lake basins 

 and valleys modified by erosion and deposition. 



The final summary of the authors suggests that the Waitaki basin is 

 due to pre-glacial erosion, faulting, with probably some warping, modified 

 by glacial action. 



After a careful consideration of the opinions of these authors thus ex- 

 pressed, one must come to the conclusion that they have regarded this 

 basin as chiefly formed in early Tertiary times, and that the Tertiary 

 deposits were laid down in arms of the sea which penetrated it at a 

 later date. 



Seeing that there has been this discrepancy of opinion, it has been con- 

 sidered advisable by the present author to consider the evidence now avail- 

 able which bears on the question, and to bring forward additional facts 

 which may help to elucidate the matter. 



In all probability the best course to pursue will be to take the case of 

 several of these basins in turn, and point out their special features. As 

 the most distinctive of these is the Castle Hill or Trelissick basin, it will 

 be considered first, and then reference will be made to the other areas in 

 turn that may be considered as likely to furnish facts of importance. 



Trelissick or Castle Hill Basin. 



This basin lies behind Mount Torlesse, between it and the more westerly 

 Craigieburn Mountains, and is perhaps the most remarkable of all of the 

 interinontane basins. • It forms an enclosed roughly oval-shaped space of 

 about five miles long by three broad, surrounded on all sides by mountains 

 which reach a general height of between 6,000 ft. and 7,000 ft. It is only 

 towards the north-east that this ring is at all broken ; in that locality there 

 is a low saddle, composed of Trias-Jura rocks, which separates it from the 

 Craigieburn district and the adjoining Micl-Waimakariri basin. 



The structure of the Trelissick basin has been dealt with by both Hutton 

 and McKay, but unfortunately neither of these geologists examined all 

 parts in detail, and there are several discrepancies between the descriptions 

 of these observers and the actual facts. In general, it appears to me that 

 McKay's account is the more correct of the two. 



The general sequence of beds, in descending order, is as follows, accord 

 ing to Hutton, and is confirmed with slight modifications by the observations 

 of McKay and of the present writer :— 



Pareora- — 



Blue shales (plant-beds). 



Soft grey sandstone. 



Grey sandy clays and shales. 



Lignite. 



Grey sandstone full of Lamellibranchs. 



Grey sandstone, curient-bedded. 



