336 Transactions. 



Art. XXXVI. — The Inter montane Basins of Canterbury. 

 By R. Speight. M.Sc, F.G.S. 



[Rend before the Philosophical Institute of Canterbury, 1st July, 1914.] 

 [For important places mentioned in this article, see accompanying map.] 



In his admirable paper on the ' ' Physiography of the Middle Clarence 

 Valley/' published in the Journal of the Royal Geographical Society, Sep- 

 tember, 1913, Mr. C. A. Cotton discusses the origin of the Kaikoura Moun- 

 tains, and considers that their main features have resulted from the following 

 sequence of events : (1) Denudation of a deformed mass of Triassic rocks ; 

 (2) deposition of the covering strata ; (3) orogenic uplift ; (4) a cycle of 

 erosion which he terms the " great denudation " ; (5) regional uplift of 

 relatively small amount ; (6) renewed denudation. 



From this it is apparent that the author considers the area now occupied 

 by the Kaikouras to have been covered by the sea in early Tertiary times, 

 and that during this submergence a veneer of relatively weaker beds was 

 laid down over these older rocks which had previously been either partially 

 or wholly reduced to a peneplain. Subsequently an orogenic uplift took 

 place, and the relatively weak beds were removed from the higher exposed 

 ridges, and were preserved at lower less-exposed levels, where they now 

 form strips occupying the floors of the main valleys and part of the flanks 

 of the adjacent ridges, or form a fringe on the seaward side of the outer 

 range of this mountain mass. 



As the author of the paper referred to applies this explanation to the 

 country to the south-east of the Kaikouras on the borders of North Canter- 

 bury, and suggests a similar origin for various important physical features 

 of that district, the present paper has been written with the object of 

 examining how far these principles may be applied to the country 

 farther south, and what modifications, if any, must be made to frame a 

 satisfactory explanation of those features. As most of the evidence bear- 

 ing on the question will be furnished by an investigation of the conditions 

 obtaining in the case of the intermontane basins of the province, a con- 

 sideration of their features is a requisite before a proper conclusion on the 

 point can be arrived at. 



We find in various parts of the mountain region of Canterbury and 

 its adjacent districts small outliers of sedimentaries of Cretaceous and 

 Tertiary age, consisting of members of the following sequence, which in its 

 complete form comprises the following, starting from the top : — 



7. Calcareous gravels, sands, and shell-beds. 



6. Sands more or less consolidated and passing downward into — 



5. Grey Marl. 



4. Limestone, glauconitic in its higher parts, and argillaceous in 

 its lower ; the lower member frequently absent. 



3. Greensands. 



2. Sands and clays, the former frequently sulphur-bearing, and with 

 large numbers of rounded concretions containing saurian re- 

 mains. 



1. Clays and conglomerates with coal. 



